This addresses issue 4738 where the Upgrade and Migration Guide link is
incorrect. This updates the link to the new Documentation site.

Missing h in highly

This is my attempt at removing similar texts from the translator work load.
It also makes an attempt at dropping some misspelled words and works toward
standardizing some phrases.

Previously, the create method was used to create a new instance of an orm
model (which would later result in an INSERT when persisted); however, some
classes require or utilize varying parameters to their create() method,
which PHP7 considers an error. Methods in subclasses must be defined with a
calling signature compatible with the parent class.

This patch shifts the concept of model creation to the constructor. Now, the
constructor of ORM models is required to be compatible with that of
ModelBase class. Now that most models do not define a constructor, this is
much easier to control, and much more logical.

Also, remove an issue where assignments on a relationship field to an
instance of a super class of the foreign model would raise an error. This
was previously addressed by re-classing the instance in the
ModelInstanceManager::getOrBuild(); however that design would create
multiple instances of the same object in memory, which defeats one of the
primary design concepts of the ORM. This patch addresses the issue by
allowing super-classes of the declared foreign model in relationship
assignments.

This commit attempts to remove all coding standard warnings emitted by PHP
7.0.

This changes the storage model for datetime fields and stores them in the
same format as the MySQL `datetime` column type. This allows for the
searching code to be consistent when searching the database for
datetime custom form entry data.

The previous code resulted in rebuilding the %thread_entry table several
times during the upgrade process. For systems will several hundred or
thousand megabytes of content in their system, this could result in a very
slow or crashed system.

This patch avoids multiple rebuilds of the table by simply creating a new
one and copying the correct values into the new table. It also avoids
possible duplicates when changing collaborators to the new thread system
considering that collaborators were not properly removed with tickets in
previous versions.

Also,
* use current year when no company name exists (yet)
* log a `created` timestamp for new files
* drop table %group during the upgrade

* Preserve external storage flag on field configuration
* User gridlayout to render task's forms
* Use new roles for task's nav

Credit: Jared Hancock <jared@osticket.com>

This patch suggests that old attachments in the `upload_dir` can be located
and left alone when upgrading away from osTicket v1.6. Later, via the `file`
command line applet, the attachments can be migrated into the database, or
to the new filesystem plugin after it is installed with:

    php manage.php file migrate --backend=6 --to=D

This allows attachment migration to be retried in the event it failed for
any reason.

* Fix crash in Ticket::getLastRespondent
* Fix crash is ORM if using a superclass of a relationship from cache. For
  instance, if the cache contains an ObjectThread instance, but a
  TicketThread instance is required in the relationship. In such a case, use
  the cached data, but change this class. This; however, violates the single
  nature of cache entries.
* Fix spurious events appearing after upgrade due to deleted tickets
* Ensure floating content in thread-body divs does not float past the bottom
* Provide an anchor to thread entries
* Show thread entries before events where both have the same timestamp
* Fix double events for collaborator additions
* Credit email sender with collaborator addition
* Fix incorrect rendering of collaborator addition event
* Fix crash on new ticket due to non-static function
* Fix missing sort on sub-query if explicitly declared in QuerySet
* Fix missing parentheses in SQL for ['field__eq' => QuerySet]
* Fix incorrect SQL on compileSelect for models with inherited $meta['table']
* Dynamically adjust relative time client side

This patch (which needs further development), introduces an extra field to
the %attachment table to store a file's name, in the event that two files
with the same content are stored in the database with differing names. In
such a case, the name is stored in the %attachment table. This allows the
attachment to specify a different name each time the same file is attached
to something in the system.

* Rename config var enable_html_thread to enable_richtext
* Copy config var name_format to agent_name_format and client_name_format
  and delete it

This stems from a bug not clearing the org_id when removing organizations

Also make forms deleteble by marking them as deleted and hiding them from
the form listing. This ensures that custom data always has a link back to
the form.