make HLTFilters global modules - part 2

convert HLTFilters into global::EDFilters (mostly) or stream::EDFilters

 - modify HLTFilter to inherit from global::EDFilter, without chaning the interface seen from children modules, except for hltFilter(...) becoming const
 - introduce HLTStreamFilter inheriting from stream::EDFilter, with the same interface as HLTFilter except that hltFilter(...) is NOT const
 - adapt most HLTFilter modules to the new interface
 - convert HLTLevel1GTSeed into an HLTStreamFilter, as it needs a per-stream internal state

this includes #1235, #1240, #1295