CopyOnWriteArrayList, to allow listeners to unregister themselves due to
an event while preventing ConcurrentModificationExceptions.
Modified all GameDataElement.elementChanged concrete implementation to
remove the backlink from the oldOne.An element pointed by an altered
element will not show the game source element in its backlink list
anymore.
!! Also, "created" elements show the "unsaved" asterisk in their
description until they're saved to disk.
Added a button to the spritesheet editor to open image in an external
tool too. This may or may not remain in the app.
- Projects can now use either loadresources.xml or
loadresources_debug.xml, or none (as before). This must be selected at
project creation and cannot be changed.
- NPC and Items comparators now include both the source and altered
version of elements present in both.
- Spritesheets view should now be better laid out, as insets were not
taken into account, thus cropping a few pixels right and down.
