Add ability to set the colour of the toggle bar on a per course basis.

I have been asked by Leonie Vos (http://moodle.org/user/profile.php?id=1435066) on behalf of a client to add in the functionality where you can set the colour of the toggle and have this stored on a course by course basis rather than editing the css for all courses.

Therefore a new option on the 'Set Layout' form will need to be added to pick the colour, then store this in the 'format_topcoll_layout' table as a new field, perhaps 'toggle_colour', then when the toggle is rendered by 'format.php' have this value applied to the toggle background.

Perhaps it might be necessary to specify the foreground colour too.