added markup and clickability to GC widget

Added markup to the displayed text so that the color can be changed during the reminder time period. Default color is red.

Made the displayed text clickable so that when it is clicked, it can open a browser page to your google calendar. Default command is firefox. The executed command can also be a script so that you can e.g. avoid opening a second tab to your google calendar if a first is already open. I've written a script that parses firefox's sessionstore.js file to do this that I'll upload to my own repository shortly.