Cache roles in columnmap
Insert roles in an intermediate step before calling class-specific component

This makes the role definitions availble to the class-specific columnmap
in $GenericMap, in case they wish to wrap them.  This is necessary, for
instance, in the case of KeyRequestors for Tickets.
Pull Requestors definition from GenericMap when GPG is off

As GenericMap is only available at runtime, and thus not in the <%ONCE>
block, move it to the <%init> block such that KeyRequestosrs functions
when GPG is disabled.  KeyOwnerName still examines $COLUMNMAP because
OwnerName is still a RT::Tickets-specific columnmap, preserved for
backwards compatibility.