Gamesetup cleanup

[elexis]

The current gamesetup needs a lot of cleanup. Commits which simplify the code and update the syntax without significantly changing the logic can be referenced to this ticket.

Refs #3049 #3355

[elexis]

In 17376:

Gamesetup cleanup. Refs #3680

Remove a broken implementation of default maps.
Remove some unneeded comments.

[elexis]

In 17377:

Gamesetup cleanup. Refs #3680

Simplify mapfilter code and mark g_CivData as const.

[elexis]

In 17378:

Simplify civ info (main menu -> learn how to play -> history).
Add JSDoc comments.
Refs #3680 a bit.

[elexis]

In 17381:

Gamesetup cleanup. Refs #3680.

Don't even load non-playable civs in the gamesetup and add sanity checks to sanitizePlayerData() and loadCivData() so that we can remove later checks.
Remove some blatantly wrong code from launchGame().
Move hardcoded romanNumbers to a global.

[elexis]

See the last 53 revisions of gamesetup.js (<= r17554).

The code is mostly readable now. Still full of edge-cases and inconsitencies that hide many bugs.

Ideally gamesetup should use the model-view-controller pattern. (One file to update the gamesettings, one file to manage the GUI objects and one file to allow the controller(s) to change the settings from the GUI). This would also solve the persist-match-settings problem.

In order to remove those inconsistencies, it would be good to have one object that holds all GUI object settings, so that all dropdowns and checkboxes work identically (see r17499 in particular).