QML UI: Allow shortcut prefixes in UI (bug 1949)

Due to the way the QML UI re-uses the search field as
URL entry field, we have to special-case additional
prefixes, so that they are properly detected in the UI.
Added (incomplete) support for The Escapist

This adds incomplete support for video podcasts from The Escapist.
The Podcast is added, with cover art and all, but the episodes still don't show up to test
if it's possible to download.
Make sure the JSON is written in canonical form

This uses the `sort_keys` functionality of python's JSON module
to make sure the settings file doesn't change when the settings don't change.
Completed The Escapist support

This completes escapist support by fixing a typo in the model and
fixing a wrong regex.