Hide multi selection option for typeahead selections

This will allow administrator to indicate if end users are allowed to reopen
tickets in a particular closed status.

Hiding a field triggers visibility check on dependent fields
Use jQuery specific value getters

This is necessary to avoid confusion vs. closed state.

Also fix crash if the [name] of a widget element started with a digit
character.

This allows administrators to define a regular expression to filter content
entered into short answer fields by agents and endusers. With the new
visibility feature, the regular expression input is only shown if the
regular expression validator is selected.

This allows fields to specify a visibility constraint that will be evaluated
in real time in the browser to automatically show and hide fields that
should be hidden based on values of other fields in the same form.

Validation is not performed on fields server-side if they are considered
invisible when submitted.

Furthermore, revamp the __cdata system to better support multiple selection
fields. Drop the `.._id` fields and use a coalesce of the ID value of the
entry value or the entry value itself. For JSON backed fields, strip some
JSON characters to result in a comma-separated list.

The search engine now uses MySQL FIND_IN_SET to analyze a search selection
in advanced searches. Also, interaction with the MySQL full text search
backend is fully supported.

Not just the SelectionField. This will make room for the InlineFormField

Attachment settings are now exclusively handled by the settings on the
ThreadEntry field on the ticket details form. Enabling attachments as well
as tuning attachment validation settings are all handled from the one place
now.

Only one file is supported at a time now; but at least the files are saved
and displayed in the event of validation errors.