Use background when instantiating from leveldata
Only render backgrounds once in LevelScreen render loop
Save levels in a proper place and allow them to be loaded
Add nullary constructors to Level and Entity Data

So that they may be loaded from json
Make certain walls and borders special
Add test_home.json (saved from game)
Remove old code for adding entities to TestScrollingLevelScreen
Add "help" command to console
Merge branch 'develop' into leveleditor