Unify use of modal dialog
Make popup dialog graggable

If a list item properties form was unable to be saved (likely due to
validation errors) properties for other list items would not be loaded
correctly (via AJAX) afterwards.

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

  * Upgrade to Redactor 9.1.7
  * Use a (x) icon from font-awesome for the dialog

*This is a major redesign / rework of the osTicket base*

This patch drops the concept of static ticket metadata and allows for an
admin-configurable arbitrary data that is attachable to tickets

The system is architected such that the base osTicket install now comes with
a "default" form that has fields for subject, name, email, and phone number.
This form is editable to allow for the addition of arbitrary other fields;
however, the basic fields must remain in order to be associated with a
help-topic and attached to a ticket.

This concept can be expanded to allow for arbitrary data associated with
registered clients or ticket thread items.

Forms are comprised of sections. Sections have a title and instructions
properties and a list of fields. Fields have various implementations to
represent different data such as text, long answer, phone number, datetime,
yes/no, and selections, and are configurable to define the look and feel and
interpretation of the respective form field.

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