Backup, i.e. rename old `Automap` / `minimap` directory

[mathiasbynens]

Ref. http://forum.tibia.com/forum/?action=thread&threadid=4503518&postid=37681995#post37681995

http://nsis.sourceforge.net/Docs/Chapter4.html#rename

We should only do this the very first time the installer runs, though. So:

1. If Automap-backup exists already,
   1. Delete the Automap folder.
   2. Else, rename Automap into Automap-backup.
2. Extract the ZIP and create the new Automap folder.