add "portable"-mode during instalation (migrated from trac, id 831 )
Original report is from Thu Feb 13 18:04:09 2014 by user: nonsinn
Original asignee for this issue is user: somebody
Add (e.g.) a file called "portable" to maxr-dir during the install process.
If this file exist, all settings nstuff should be saved in a sub-dir of the game-dir instead of the 'users' dir