Merge pull request #3 from M7S/dbx-devel

Make the dockbarx plug way less hacky thanks to refactoring in DBX devel version.
Merge pull request #4 from M7S/dbx-devel

Use the correct get_container() function instead of manually using group...
Fix for issue #9: changing theme makes xfce dock disappear. Fix requires DockbarX 0.91.2.