This patch fixes an issue where a fatal error would be triggered if the
current value of a selection field on a custom form was a custom list item
that has since been deleted.

Also add some logic to the POT builder to warn about incorrect arguments to
the __() function and friends as well as warn about _() usage.

When managing properties of list items

  * Paper sizes
  * More prompts on ticket filters

This patch fixes a glitch in the dynamic forms processing system preventing
the validation and capture of data for help topic custom fields. Now the
`$vars` managed inside of `Ticket::create` is connected directly to the
`DynamicFormEntry` created for the data rather than using the magical
connection to `$_POST`.

Add multiselect  option to selection and choices fields.

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

Generalize custom list interface in order to provide for facility to manage
system's built-in list like ticket statuses, priorities ...etc.

Several places in the code initialize a list of objects from the database
and only fetch one item. In certain instances (which seem almost like a race
condition), MySQL will feel like there are more records available in the
database and will complain with "Commands out of sync, you can't run the
command now".

This patch addresses the issue by utilizing the ::one() method of the
QuerySet where only one record is expected. The ::one() method is further
designed to fetch all one results (which satisfies the MySQL client library)
and return the first item.

That patch introduced a bug where the list of dynamic fields for a form is
always empty

New ticket by staff would cause the %{company.name} variable to be
incorrectly replaced as the user's name in email templates.

Otherwise, no column will be added to the %ticket__cdata table and the
ticket queue pages will be crashed (empty).

Allow developers to specify a sorting position for groups of fields
selectable in the criteria select drop-down

This is necessary to allow for other form types to use dynamic data
view/export