EXP-1021 FIX Position of web content browser dictates position of profile panel - profile panel position changes do not persist
EXP-1030 FIX Search button toggle can get out of synch in bottom bar
made llinstancetracker::iterator do own nested level management (removing need for separate guard)
added support for filename= to floaters
can pass in arbitrary window_class to floaters

move LLEventTimer into its own source module.  everyone includes it, almost no-one wants it.  now I can dick with it a bit without rebuilding the world, at least. :)