Fix the working directory for shortcuts created by the Windows installer

In NSIS the working directory for shortcuts is controlled by the SetOutPath variable, see http://nsis.sourceforge.net/Docs/Chapter4.html#createshortcut . In our case this caused the working directory to be set to the "locale" directory.

Fixes [PICARD-649](http://tickets.musicbrainz.org/browse/PICARD-649)