Resource Store & Cleanup

Added: There's now a resource store which loads resources into the game before it starts. That should fix the bug which sometimes happened and stopped loading the map.png-file.
Fixed: Some housekeeping (method visibility, small style improvements etc.).
UI updates & fixes

Added: Custom scroll pane & (tree) table.
Fixed: A frame doesn't look messy anymore (made the title bar smaller).
Added: You can now provide the theme file for a graphics state with an URL.