AppConfig path handling changed.

The AppConfig path will now be OS depandant:
Windows:

Path.Combine(Application.CommonAppDataPath.Replace(VersionHelper.GetAssemblyVersion(),
string.Empty)

Linux:
Path.Combine("$HOME/.ksp_mod_manager", Constants.APP_CONFIG_FILE)

OSx:
Path.Combine(Assembly.GetExecutingAssembly().Location,
Constants.APP_CONFIG_FILE)