Add a tab for tasks
Add mass action for tasks

This patch rebases filters into a row-based layout and redesigns the filter
apply method to be more extensible. It also redesigns the UI to be more
dynamic and to allow for actions to be added without database modification
and actions can also have complex configurations.

Help topics can now specify one or more additional forms to be included on
the help topic and can also specify the sort order of those forms.
Furthermore, individual fields can be disabled per help topic, so that
unnecessary fields can be omitted when necessary, per help topic.

The disabled flag is recorded along side the field data so that the field
will not be accidentally added to the form later automatically. There is no
interface in this commit to enable a field which was disabled by the help
topic when ticket was created.

Add ability to add tasks to tickets.

Introduce the initial concept of adding tasks to a ticket.

The solution is simple: upload the image, create the draft automatically,
attach the image to the draft, return the draft_id to the client. That's it.
There's no more need to create the draft in advance now.

Show different messages and placeholder on ticket(s) deletions

Move ticket status change to unified backend.

Also add a drop-down list of common links include ticket links and login
pages for both agents and end users.

Ticket numbers are now configurable as a system-default and by help topic.
Previously, an administrator could select between six-digit random and
sequential numbers. Now, the sequence is selectable so multiple sequences
as needed, and a format can be specified to define how the ticket numbers
look. Formats can also be defined for each help topic.

Add an interface for custom list items.
Implement CustomListItem for built-in and custom lists.

Add original and last message quotes to canned responses

Show user search box when adding a new user

Support adding remote user to an organization

Support adding existing or new users while on organization page.