removed db code from TestTrackTools, should instead create TrackViews directly
removed __len__ from NDARRAY_SPECIAL_METHODS_TO_OVERRIDE because it's implemented in all subclasses
update_offset doesn't need return self
now using 'is'/'is not' instead of '=='/'!=' because they do not call __eq__, which caches numpy array in VirtualTrackColumn
created functions for deciding track type in TrackFormat
possible fix for inserting into existing table with larger shapes
refactored 'set offset' in VirtualTrackColumn. slices cached array if possible and deletes it if required
Merge branch 'pytables' of github.com:brynjagr/gtrackcore into pytables

Conflicts:
	gtrackcore/tools/TrackTools.py
changed more '=='s to 'is's
refactored coverage function to use TrackFormat's track type functions