datetime: add -lm to libraries
info: Remove GNOME version data parsing code

We don't use this anymore.
info: Remove PackageKit-based updates UI

We don't use PackageKit, so we don't use this. We'll add our own OSTree
updater checker here.
info: add a way to check for manual updates

Coordinate with the OSTree daemon to manually check for available
updates and possibly install them.
Merge pull request #20 from endlessm/shell/3678-v2

Shell/3678 v2