user selection: MDL-17072 Polishing the role assign page:

user selection: MDL-17072 Polishing the role assign page:
* Make the role being assigned clear in the title
* Make the options in the middle of the page be in a collapsable options section, collapsed by default.
* Put them in a smaller font too.
* Switch the date selectors here to use a shorter date format, and change 'Course start date' to 'Course start'.