Fixed up for latest gmail interface

Two small changes. Firstly it assumes everything with the class .editable should have the font monospace. The only quirk this produces is when you compose an HTML email, you will compose in monospace, but the UI will show your current font as Sans Serif. This is just a confused UI issue though - it sends without any style information added, so the receiver will just display using their default font, which seems to be the right thing to do.

The second change is I removed the colour override for quoted text, since gmail does threaded colouring now.

Now my pull request is about the length of the script :-)