Include color set names in outputted themes

[mjswensen]

Other feature request

Problem

Themes outputted by themer do not have unique names, so only one themer-generated theme can exist at a time.

Solution

Color set names (like default or solarized) should be included in the outputted theme files, so that users can easily switch between themer-generated themes without name/filesystem conflicts. Themes generated from custom color sets should use a short hash of the colors, or perhaps a custom name field.