[enhancement] Add application icon to title bar in Ambiant-MATE/Radiance-MATE themes

[Michael von Glasow]

So far, when choosing the Ambiant-MATE/Radiance-MATE theme and a layout which puts the Minimize/Maximize/Close icons at the right end of the title bar, the top-left corner has just a dot icon where many other themes place the application icon. This is presumably a legacy from the original Ubuntu theme, which always had the controls in the top-left corner and thus never bothered about adding an icon there (and had the same dot if the controls were moved to the right). With MATE giving users the choice, I’d consider it an improvement to have the icon.

I had once forked the layout and added the icon, which I remember was fairly easy. However, the changes from 16.04 to 18.04 are so extensive that I ran into a bunch of merge conflicts. If it helps, you can find my previous work at https://github.com/mvglasow/ubuntu-mate-theme/tree/revamped.

[Martin Wimpress  (flexiondotorg)]

Please submit a pull request against https://github.com/ubuntu-mate/ubuntu-mate-artwork