Ember now conforms to the XDG spec

I’ve just pushed some changes to the Ember client which makes it conform to the XDG Basedir spec.

The main difference is that the ~/.ember directory isn’t used anymore. Instead configuration files are put in ~/.config/ember while data files are put in ~/.local/share/ember.

During startup the contents of ~/.ember will be migrated, and a backup will be made in ~/.emberlegacy.

Many thanks to Olek Wojnar for making the bulk of the changes.