MapGen: Proper "create game" UI

[Katharsas]

The UI for selecting map should be support 2 use-cases:

• User wants so select or random a handmade map from list
• User wants to generate random map with specific settings

Only in the first case it is necessary to show a map list.
Only in the second case it is necesary to show generator options/settings.

The generator-specific UI elements are / could be:

• Select number of player spawns (only 3v3 currently)
• Button to generate map / regenerate with current settings
• Checkbox and input: Generate from seed / name (input for seed/previous map name), greys out other options.
  Optional:
• Show a list of recently played seeds/map names.
• Change biome (optional)

So we need some kind of tabs, kinda like this (but of course withg different look)

[Katharsas]

Part of FAForever/Neroxis-Map-Generator#35