This fix a problem when you proxy the matterhorn server

This fix a problem when you proxy the matterhorn server in an URL that is not the root folder of the server.

Our MH server has an URL like http://proxyserver.com/matterhorn
This works ok in Galicaster 1.3.x, but in Galicaster 1.4.x it's not working because Galicaster try to call to
http://proxyserver.com/recordings/calendar instead of http://proxyserver.com/matterhorn/recordings/calendar
This pull request solves this.