Short Game option

Adds a short game lobby and map option. 

The short game is basically what we already had, players need only destroy an enemy's base buildings to win. In a "long" game, they need to destroy (almost) all enemy units to win. The exception are cloaked units and buildings (that is, those that are cloaked by default, not upgraded ones), which are not taken into account.

Also fixes #6589.
Because 1) otherwise this wouldn't be an option anymore (ie. you'd have to specify it in the options stanza of a map.yaml), and 2) the other options are set up the same way (this whole thing, or at least the c# parts of it, is basically just a copy&paste job)