main changes are:
- Modified marker (* character before name) goes up the project tree by
marking all parents of a modified object as modified.
- Impact management when changing an object's ID. Allows for some
refactoring to occur, while marking the impacted elements as modified,
or aven creating "altered" versions if imapcted element was only in game
source.
data using a thread-safe collection. Some NPEs fixed.
More data protection in tiled integration functions (better state
checking, backup tiled-made file before saving ATCS-made data).
jardesc file added for convenience.
