Add override overview ruler color option

[stneveadomi]

I think a good default option for the overview ruler option is to take either the background-color or color and map that onto the overview ruler.

We should add a checkbox above this and disable the input box unless the override is enabled.
Precedence of fetching color:

IF OVERRIDE

1. Background Color
2. Color
3. No value

IF NO OVERRIDE (BUTTON SELECTED AND INPUT AVAILABLE)

1. Default is input box entry
2. If empty, no value.