Allow GutterColor on every file type

[nachocab]

Hi, great plugin!

I often want to see the color in other files besides CSS (for example, javascript, R, or python files). I can see the colors by temporarily switching the syntax mode to CSS and then switching back to the original one, but there must be a better way.

Also, is there a way to switch the colors off?

[jbrooksuk]

I mentioned this in #42 - if we change the plugin to allow extra scopes to be added where needed we could add a condition that if no scopes are entered, run on everything.

[nilssolanki]

+1 This would be great, because we have some color definitions in Javascript too.