Only update current doc & CSS append once

Now only updates the innerHTML value of the stickyTab doc if the browser
location is the same as the doc we're editing (HTML & MD files). Also
now adding an ID to the style and if it exists, remove that child DOM
elem before adding another so we only ever have 1 child for this, ie, it
gets updated by removing & adding.
Don't reload MD files

Stick with the Markdown parsed version shown via editing.