Continuous build

Merge network and local game scenario selection list

The UI now deactivates and activates the option buttons for league,
password etc. The network button now has three states (two in the lobby):

- singleplayer game (only when not in the lobby)
- local network game
- internet game with masterserver signup

Each state changes the network settings in the configuration, keeping
the previous behaviour.

An additional feature is that all scenarios can now be started in
singleplayer regardless of there max player count; lacking enough
players, a warning message is displayed.