[FEATURE] Allow setting of color theme manually vs solely with wallpaper

[dwilliam62]

Is your feature request related to a problem? Please describe. Sometimes you select a wallpaper that you really like but the resulting colors for terminal, borders, etc isn't what you like.

Describe the solution you'd like Currently the wallpaper rofi menu sets both background and theme Maybe a pure theme option using that same process. Maybe even a checkbox on the wallpaper rofi menu to both set background and theme environment

Describe alternatives you've considered What I do now, is at the CLI. run ```wal -i IMAGEFILENAME`` and try random images. Sometimes the results are quite interesting or dramatic