Change color of UI elements

[vitalykorolev]

Optionally, allow user to change color of UI elements such as window buttons, check boxes, bullets, etc. This can only work with themes that use SVG for the graphics. (such as Numix and its derivatives)

For example, I can run the following command in the theme folder to make the change. grep -ril '#d64937' | xargs sed -i 's/#[d|D]64937/#3465a4/g'