Added xscreensaver-gl and xscreensaver-gl-extra
Summary: Added xscreensaver-gl and xscreensaver-gl-extra
Test Plan: After this, check if flurry is default theme for xscreensaver
Reviewers: tsimonq2, wxl
Reviewed By: wxl
Maniphest Tasks: T21
Differential Revision: https://phab.lubuntu.me/D59