some bug-fixes, enhancements and performance improvements

NOTICE
	this update needs deleting the old epg.sqlite manually due to database changes
	maybe there will be an automatic mode for this in the future

modified database to enhance performance
	changed table layout
		switched from start/duration to start/end
		less calculations
		better indexing
	removed old prepared statements
		might speed things up a bit

switched to a flexible lookup statement
	allows combination of several parameters
		e.g. time and search-string
	will provide additional features in the future
		e.g. for timeline interaction as requested by issue #1

removed "by program" from the navigation menu
	added this functionality into "on air"
	this addresses issue #2