CF tabs in Queues' admin interface

Put "Ticket Custom Fields" and "Transaction Custom Fields" page
tabs under one "Custom Fields" tab. Page tabs were just two wide,
so in some translations it could quickly become two line instead
of usual one and hide content.

Top "Custom Fields" tab is not linked as I feel that for a queue
it should link to a list of queue's custom fields, but we don't
have such page as these custom fields are global. Linking to
Global -> Custom Fields -> Queues is an option, but I decided
not to go there.
Merge branch '4.2/cf-page-menu-in-queue-admin'