Updates drawer to work from both sides and adds background transitioning

[brybott]

No description provided.

[gregor-srdic]

thank you for your commit, however I still see the following problems:
you can not use both left and right drawer in the same view (isolation of the directive scope solves that),
and removal of overlay is not animated, but happens instantly (opacity is animated, but it is instantly hidden, so the effect is not visible)