Gamesetup: Disable the "Disable Treasure: Disabled" double negation

[elexis]

The double negation of the gamesetup option "Disable Treasues: No" is subideal and I recall sanderd17 not being too happy about it too:

From 2016-04-30-QuakeNet-#0ad-dev.log: 16:04 < sanderd17> * Disable treasures: no > looks awkward to read IMO.

The issue became worse with the objectives dialog that has the double negation "Disable Treasures: Disabled" and some players have trouble understanding what it means.

To alleviate the issue, we can add a new Keywords entry to all maps that either start with treasures or have a trigger script spawning treasures (currently only survival of the fittest).

Then the "disable treasure" gamesetup option could become a "treasure" option and the user selects a map that doesn't come with treasures, that option could be hidden altogether.

The icing on the cake would be adding a new mapfilter to select only maps that come with treasure. The filter would be nice to have as treasures have a significant impact on the gameplay (turbo start, but can also imbalance the game if one player takes it all); and there are no negative impacts of having such a mapfilter.

[Palaxin]

refs #4374

[Imarok]

Move tickets to Game Setup as UI & Simulation got some sub components.

[Freagarach]

Probably fixed by the GameSetup rewrite (r23374). Actually r19652.