Show available maps in alpha gui

[robotanarchy]

This should be done by parsing the available maps. Other tools created by the GTA2 community can already do this, so it shouldn't be too hard to implement here, too.

[robotanarchy]

Same as #2 : "Fixed in 0.3.0 by just displaying the normal hosters dialog. No need to replicate everything for an autoit gui - this will become interesting again in case we make that fullscreen controller compatible SDL gui."