tweaks and comments
minor cleanup
cleanup IconCache and rename to  ThumbnailCache
move functionality from ImageAnalyzeController to GroupManager; simplify threading
improve usage of progress bars to represent actual bg tasks
fix bug in slideshow cycling
Merge branch 'documentation_and_cleanup' into timeline_and_image_analyzer
cleaned up FileUpdateEvent
cleaned up ImageAnalyzerModule
clean up OptionsPanel
cleanup Topcomponenet
Merge pull request #871 from millmanorama/timeline_and_image_analyzer

Timeline and image analyzer