Partial work on asset refactoring
Merge with upstream
Load assets on program start and persist them globally. Completely reworked object/tile asset handling(WIP).
Include missing files
Add some platform image support.
Don't reset view when switching layers in the same part
Change graphics/bitmap settings for slightly faster rendering.
Proper use of disposable. Fix bug where no object direction specified causes its drawing to fail.
Enable some properties for editing.
Merge remote-tracking branch 'upstream/master'
Fix object orientations again, add workaround for flipped objects
Load assets in another thread.
Merge pull request #5 from heinermann/master

Asset file handling changes (round 2)