Cinnamon 3.4.0 support

[oberon-manjaro]

I just opened a pull-request updating vertex-theme for latest Cinnamon Deskop 3.4.0, supporting vertical panels and other recent Cinnamon additions.
Since this theme seems to be orphaned I don't expect it to be merged, really 😉 but in case anyone is interested you can either use the git diff to patch the source or you can just build it from my fork if you like (master branch there also includes some other unmerged patches from the original repo here).