Keymaster's Keep: add Monster Rancher 2 DX and add unittest

[Silvris]

MR2DX support, nothing too crazy there.

Unittest simply just tests that the objectives of all games (optional + regular) return as string, which should hit all relevant code paths.

[nbrochu]

I would politely request to stick to games only for PRs, as highlighted in the contribution guidelines.

Updating the supported game docs ahead of time, while obviously done with good intentions, is not useful. I generate them once before release and like to look at the diff to do the credits. Also, it would show right away in the documents people refer to for the current release.

And the tests do not cover all paths since more and more games pivot on AP options to dynamically assemble the list of game objective templates. I simply don't want unit tests this early on something that will evolve quickly and where entire concepts might be thrown out the window with no notice. I'm a fan of unit tests when things are more stable, not as-you-go.

I do appreciate the implementation for a great game though. Thank you.