Merge pull request #123 from somini/master

Adds support for The Escapist Video podcasts
Gtk UI: Keep reference to last "add podcast" dialog (bug 1021)
Install scheme handler for gpodder://, feed://, podcast:// and pcast://

This allows subscribing from within a webbrowser by linking to
gpodder:// (and then the full URL of the feed).
Fixes error that brok other downloaders

This fixes an error where downloading non-escapist URL resulted in an error.