This addresses an issue where disabling Ticket Locks but setting a time
for the Lock Timeout will always throw a "lock required" error. This adds
a check to see if locks are enabled AND there is a time set. If locks are
disabled it will not throw the error.

This feature adds a setting to the control panel to require signing in to
view attachments. This is in addition to the security already provided in
the download URLs. Currently, download URLs are signed for a specific help
desk, and automatically expire after about 24 hours. The exact timing is the
following midnight allowing for at least 12 hours cache time.

Administrators can impose this extra security feature to refuse serving
attachment files if the user is not currently signed in. This could prevent
third-party users from viewing an attachment if they were able to get access
to the download URL before it expired.

Make config items caching class instance based.

This duplicates the custom logo code to allow for custom login backdrops. A
new page is added to the "Company" settings page which allows for management
of the uploaded custom backdrops.

Also, rename other apc_xxx functio to the new apcu_xxx equivalents available
since PHP 5.4.

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

Catch InconsistentModelException on config load to allow for fallback to old
config table when upgrade is pending.

Fixes #2751

Add ability to disable use of authentication tokens on ticket links

Add a global option to disable avatars on thread correspondence . Agent's
and user's profiles will still show an avatars.

Support using global config table to store agent's preference.

Move setting from Setting > Tickets to Settings > Agents

Fixes #2433

Initially, include support only for Gravatar

This allows messages to be stashed in the session and displayed on a
following request. This will be pivotal in implementing the PRG
(post-redirect-get).

* 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

Add Agents and Users setting pages
Move global settings to System settings

This patch attempts to query or detect the Olson style timezone
(e.g. America/Chicago) from the database. This is preferred over the
previous code as the previous code would always consider the current
database GMT offset rather than the GMT offset of the date being converted
(which might be on the other side of a DST transition).

The setting is no longer ticket thread specific. Disabling html is now
system wide setting for disable-able textarea widgets as well as email
correspondence.

Settings for storage backend and general max size setting for agents

Add initial concept of activity alert/subscription model to ticket activity.

This patch converts the central file and threading classes over to use the
ORM.