Follow XDG basedir specification

[Lucki]

Right now a new folder for configurations and userdata is created in $HOME/.megaglest.
To be more flexible it would be nice to implement the XDG Base Directory Specification.

$XDG_DATA_HOME defines the base directory relative to which user specific data files should be stored. If $XDG_DATA_HOME is either not set or empty, a default equal to $HOME/.local/share should be used.
$XDG_CONFIG_HOME defines the base directory relative to which user specific configuration files should be stored. If $XDG_CONFIG_HOME is either not set or empty, a default equal to $HOME/.config should be used.
$XDG_CACHE_HOME defines the base directory relative to which user specific non-essential data files should be stored. If $XDG_CACHE_HOME is either not set or empty, a default equal to $HOME/.cache should be used.

An easy explanation can be found in the gnome wiki.

This would result in the following folders:

• $XDG_CONFIG_HOME/megaglest/<GLESTUSER.INI|GLESTUSERKEYS.INI> defaulting to $HOME/.config/megaglest/<GLESTUSER.INI|GLESTUSERKEYS.INI> when $XDG_CONFIG_HOME is not set or empty.
• $XDG_DATA_HOME/megaglest/<MAPS|SAVED|SCENARIOS|SCREENS|TECHS|TILESETS|TUTORIALS|DEBUGWORLD.LOG|GLEST.LOG> defaulting to $HOME/.local/share/megaglest/<MAPS|SAVED|SCENARIOS|SCREENS|TECHS|TILESETS|TUTORIALS|DEBUGWORLD.LOG|GLEST.LOG> when $XDG_DATA_HOME is not set or empty.
• $XDG_CACHE_HOME/megaglest/<CACHE|TEMP> defaulting to $HOME/.cache/megaglest/<CACHE|TEMP> when $XDG_CACHE_HOME is not set or empty.

Advantages are:

• No predefined paths. The user can decide where his or her data is located.
• No cluttered home directory. Some selectors will automatically show dotfiles, finding the files you want will be easier.
• A shared storage location for data. Application data does not have to be searched for, as these are no longer located in different places. This also benefits a backup.
• Resetting the settings and keeping the application data at the same time becomes easier, as there is a clear separation.