[cinnamon 3.2] Support for vertical panels

[jeweloper]

Cinnamon 3.2 has now the possibility to add vertical desktop panels.
Currently these vertical panels are transparent and missing the standard theme color.
Another problem is that most of the applets are not positioning in the vertical center. Some of them also overlapping the panel border.

[jeweloper]

@lots0logs I would like to help to fix this issue. But some parts that codes the panel customization is written in sass whereas other parts are written directly in css. Which language should I choose to implement the fixes? Thanks for your answer.

[lots0logs]

@jeweloper I've been wanting to reorganize/semi-rewrite the cinnamon theme for a while. I think now is a good time to do it. I started working on it yesterday. You can see what I've done so far on master branch here. Its still a bit of a mess but the goal is to use sass throughout and eliminate unnecessary usages of svg images for styling elements while reusing as much as possible/appropriate from the gtk theme.

From the current state, I think we can start by simply replacing color variables throughout to use the equivalent variables from gtk theme and perhaps eliminate some of the svg usage (though I dont think there will be enough time to properly remove all of the svg before publishing the next release)

[jeweloper]

thx for your answer. I will have a look...