semi playable units

[DreadKnight]

When enabling a new unit for development, a developer could only be poking at a certain ability, which would be problematic. Even worse, the other abilities would probably be unusable. We should handle such scenarios better, in order to improve testing.

Possible solution would be to have another option for the playable field from data.json file, that will mark units semi playable.
All these beta type of units will only actually be enabled in the development version of the game, being able to unlock / materialize them by holding shift key while in the dash screen during Dark Priest turn that can actually materialize. That way it will be harder for noobie testers to materialize and try to use any of the units that are being worked on and aren't yet properly ready for masses.

[DreadKnight]

This is related to #2184