#14 Command to merge projects

[Rainer Deyke]

Occasionally I create multiple TileStudio projects,
only to later find that I would rather have only one
project file. This problem could be solved by adding a
command that loads a TileStudio project file and merges
it with the current project. If both projects include
a tileset with the same name, there should be an option
to either rename one of the tilesets or to merge them.