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