Filter assignees based on selected tickets department setting.

Filter members based on department's assignment restriction when building a
list of assignees.

ClaimForm extends AssignmentForm and hides assignees selection. Claimant is
still given the opportunity to log an optional internal note as to why
they're claiming the ticket in question.

Let the object have full control the list of possible assignees

Due to MySQL FULLTEXT min-word-lenn requirements (which various from
installation to installation), fulltext-based searches require at least two
characters.

Otherwise we might end up with a search term like '"some junk"*' which is
invalid.

This time, use full-text for user and ticket lookup boxes, and drop the
full-table scans from the ticket basic search page. Auto promote searches to
wildcard searches when searching with the user-supplied input yields no
results.

Also, fix submission without a lock and locks are disabled

- Adds mass assign, transfer to ticket queues
- Retire inline forms for ticket assignment and transfer

- Tickets cannot be closed when an open ticket exists
- Tickets/Tasks cannot be closed when required for close fields are missing
data
- Add isCloseable routine to ticket/task classes

Initially, include support only for Gravatar

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.

This patch removes several of the internal notes posted to a ticket for
various events and replaces them with events added to a threads event chain.
The emails are still sent out as they previously were, but internal notes
are only added to the thread if an agent actually specified comments.

Move collaboration implementation to thread level

Reset field content when building a new form

Also, add warning popup when lock is about to expire and allow the user to
attempt to renew the lock. Also, connect the keyup callback for redactor to
the autoLock.handleEvent for greater update of the lock, and also deadband
the lock to every 10 seconds.

This patch includes a slight database migration, and adjusts the
functionality of a few core components.

  * Move collaborators from the ticket to the thread.
    This concept allows collaborators on any object which has a thread,
    including tasks.

  * Add flags to the thread entry
    This will allow flagging thread entries for different purposes.
    Initially this can be used to flag the original message of a thread in
    case a ticket / thread is created without an initial message.

  * Lock becomes more of a utility
    The lock is now disconnected from the ticket and is a separate utility.
    Separately, the ticket and task objects can have a reference to a lock
    object. Furthermore, when submitting some activities to tickets, the
    lock is verified to be owned by the respective agent, and the lock code
    must match a current lock code. The code is rotated on each acquire()
    call to guard against double submissions.

  * Collaborator is an ORM model
    The TicketUser class is broken up now so that the collaborator instance
    can exist apart from a ticket. Email message ids are now generated for
    collaborators without respect for a ticket so that collaborators can be
    properly supported on any thread.

Don't add to endTime if not already set

This patch changes the default formatting for text bodies used in emails,
ticket thread, and canned response quoting so that white-space in text
bodies is properly preserved. Previously, the text was treated as raw HTML
and was not properly escaped, nor was the original whitespace preserved.

This allows agents to view the raw email headers parsed with the email when
the ticket or thread entry was created.

Allow for permissions to be registered dynamically. This will
allow for the ability for models and plugins to register permissions.

This resolves #1570

Add ability to add tasks to tickets.

Introduce the initial concept of adding tasks to a ticket.