#139 Autosave file path setting

[Magnus Beischer]

The autosave file location is not settable from the application. I want the autosave feature, but at the same time I don't want to clutter the normal directory where I keep the tinycad file and other files that all are under version control (Git and Subversion).

Propose that we add a feature where the user can choose the path to where the autosave file is stored.