controller: make gear UUIDs predictable

Introduce an option that creates gear UUIDs based on the app name
instead of the standard 24-char hex format.
Enterprise use case:
https://trello.com/c/bUe7eOL6/290-enable-predictable-gear-uuids-ose
controller: option LIMIT_APP_NAME_CHARS

This option is related to USE_PREDICTABLE_GEAR_UUIDS in that it allows
the administrator to restrict the inputs for predictable UUIDs by
rejecting app names that would be too long to make UUIDs.