Adds new header option "HeadlightsTabString"

[ajskelton]

I've been using the CodeBlockPro block on a client site and they had a design request to have a 'tab' like title for the filename in the header.

I combined the Headlights and SimpleString headers to create a new header type "HeadlightsTabString". I also used the HeadlightsMuted background color for the header, and then pulled in the background color of the main editor to use for the tab background.

Here is an example of the new header:

If you don't want to include this in the plugin is there a good way to extend the plugin to add in custom headers?