update CategoryCounts, FollowUp and Category border on general Tag Event
use most severe category if multiple categories are present for a file
enforce category ordering via enum declaration order
rename and comment DrawableViewBase
more cleanup of category related code
comments
license header; cleanup in DrawableDB, GroupManager, and ImageGalleryController
cleanup HashSetManager and DrawableGroup
cleanup/commetns DrawableTile, DrawableView, DrawableViewBase
more cleanup ind DrawableDB
