Fixed Group identification of Air Force pilots

Fixes #669.

Few minor fixed related to flatpak prepare

Make 2.0.0rc2 tag

Set version in CMake 3.x style. We need that version anyway for C++11
standard.

First 2.0.0 release candidate

Fixes failing builds on 32 bit platforms. Makes compatible games over
network.

Include build version in game

Fixes several string formatting errors.
Update icons and help.

Version 2.0 prepare, show version in-game

Version did not show in game anywhere. Include it in credits.

Upgrade version information to 2.0.0

Keep this version as alpha yet.
Add make tag target to simplify tagging of new versions.

Old sources imported from 1.1 archive

Old sources imported from 1.0 release archive