Added arg to specify path of cfg/tmp files

[CityofSirtel]

Behaves exactly the same if no Remnants.cfg is not provided or does not exist. Allows .jar to be called from system wide install with no write permissions, and save/cfg/temp file directory in user folders, like $XDG_CONFIG_HOME

[Xilmi]

Indeed, the initialization of the new path is done too late.
Consequently, the new path is called twice before being initialized!
leading to a possible crash when chosing a Bitmap galaxy and trying to select a file.
in rotp.java: Moving "UserPreferences.setCfgPath(cfgFile);"" to line 143 only solve half the problem!
The UserPreferences class initialization request a call to this path! There is no way to place this basic parameter in UserPreferences... It must be located in rotp.
I would recommend declining the pull request!
Notes:
This is a complex change for a non issue: Just placing the game file in a writable folder solve everything!
I wouldn't want to encourage continuing in this direction either:
Currently, placing the game in the wrong directory results in a simple question and a simple answer, solving the problem.
With these kinds of changes, new users might not be notified and would unwittingly become beta testers... This will probably lead to a lot of problems, because the basic testing hasn't been done thoroughly enough!