Test refactorings and reprioritization.

Adds more feature specs for the Ticket resource, and removes redundant
controller specs that cover the same functionality. The TicketController
spec now compliments the set of Ticket feature specs, and focusses on
access control issues.

The validations and associated tests regarding the presence of a Ticket's
associations have also been changed from _id oriented tests to actual
association instance presence tests. This gives a better indication of the
presence of the right type of thing, and also brings into play the
inverse_of hint which can be handy in some scenarios.
Feature spec description tweaks.

A few small changes to make the naming scheme of the feature
examples more consistent.