console color scheme selectable (default dark)

Console color scheme can be selected from a menu that appears with a right click.
Available schemes:
- Dark (dark background with light fonts) - default
- Light (light background with dark fonts)

Also needed https://github.com/tanmaykm/shellinabox_fork/commit/8d2a31df39e3097bcf5e56e6252372655233ca11
and https://github.com/tanmaykm/shellinabox_fork/commit/8e3a8c2943c97dea98621236cfbc7c20aedcccf7

ref: #67