Fix to display properly in our custom theme

Hello Daniel,

First, thanks a lot for sharing this plugin. Upon testing in various browsers (IE11, Safari 8, Chrome 39, Firefox 34, Android 4.4, and Safari mobile 8), I noticed that the plugin works flawlessly when using Moodle's Clean theme, but not when using our theme. Using our theme, the editor didn't resize to the whole window properly.

So I make a few modifications, which make it work perfectly in our theme without disrupting the result in the Clean theme.

Would you consider merging my changes with your code ? Basically, I use fixed CSS positioning to force the editor to take up all the space in the window.

Thanks,
Nicolas