Allow changing install location on reinstall

I wanted to move Dopus to a different folder, but the installer doesn't have this option if you already have dopus isntalled 9only on fresh install can you pick a location).
Other installers usually allow you to do that, and DOpus' should as well.

(this led to data loss since I uninstalled / installed again, but Dopus has a bug that deletes all data on uninstall without the possibility to disable it and even without a strong warning Uninstall removes scripts)