Mint-X caja file manager side pane color fix.

[mdinslage]

Disregard this post, the code has already been merged.

Forgive me if this is already planned, I know this is a work in progress, but I just installed Slackware64-current in a virtual machine. I am running Mate 1.20 with GTK 3.22. On my machine the caja side bar background is white and not respecting the previous color settings. Adding this code to the "mate-applications.css" in the caja section fixes the problem.

.caja-side-pane notebook treeview.view,
.caja-side-pane notebook textview.view text,
.caja-side-pane notebook viewport.frame,
.caja-side-pane notebook widget .vertical {
    background-color: shade (@caja_sidebar_bg, 1.0);
    color: @caja_sidebar_fg;

Also forgive me for not submitting a pull request, I am trying to fix various issues I find with Mint-X and Mate, but I am not as acquainted with Gtk 3.2x framework as you probably are. I have a few more I am working on and I will post them here in "issues" for your input if that is ok?