Add loading ckeditor.css from theme.

Hello,

I've been really pleased as to how the ckeditor module is somewhat "smart" about applying a theme's css within the editor. When you choose "use theme css" for the editor css option (admin/settings/ckeditor/edit/profilename) it aggregates all the theme css files it can find... across base and subthemes, etc. This is great.

However, getting your own custom css "overrides", that apply just to the editor (force the background to be white, etc...), is still a bit tricky. Sure you have the config.extraCss js configuration variable, and you can always manually define your own editor css files, but it seems to me that is would be handy if ckeditor automatically looked in your active theme directory for a "ckeditor.css" file, and also factored that in when you choose the "use theme css" option. It already checks for a "ckeditor.css" file in the module directory, so why not look for on in the theme's directory too?

It's nice to have the option to keep everything tied to the active theme, and it's always nice to avoid lots of js customizations and tweaks. I've also found that the config.extraCss js configuration variable has some limitations (see #834228: Need to change background of toolbar dropdowns using theme css & Kama skin) and that there is no easy way to manually set your editor css to be smart about base/subthemes (without defining absolute paths) in the way the "use theme css" option does.

Anyway, the attached (tiny) patch tells ckeditor to also check for a ckeditor.css file in the active theme if the "use theme css" option is selected. Does anyone else see a value in this?

Ryan