Merged l1t-devel-CMSSW_7_2_0_pre5 from repository cms-l1t-offline
Move plugins to own directory

One should not put plugins into libraries. Instead, plugins should
be built directly into shared plugin objects.
This fixes the problem in the IB where L1GlobalTrigger module could
not be found. It could not be found since the library it was contained
within was no longer being indirectly linked to some othe plugin.