Editor: batch-resave all project rooms in the latest format

[ivan-mogilko]

There's a curious problem related to upgrading older projects. AGS 4 has older version support cut, and the user must rely on the latest backwards compatible version (3.6+), and upgrade the project in steps:

• open in v3.6+ and save;
• then import in v4.0.

The project itself is easily upgraded: loaded up in the editor and resaved. However, rooms are separate files, and they are not resaved after loading a project. Furthermore, it's even not enough to open them by hand and hit "save", because apparently editor does not write anything disk unless some data was modified. Some projects may contain hundreds of rooms, making any manual operation tedious.

I propose implementing a "resave all rooms in project" operation, and decide when it's run. This may be a either an explicit command in the File menu, or an automatic action after loading an older project.

OTOH forced upgrading and resaving all rooms on project import may be desired because in theory there may be troubles when mixing rooms of different versions in the same game.

[ivan-mogilko]

I had a moment of silliness, all this may be solved by doing Build -> Rebuild all files.