Weekend Time/57 -- Don't display time on weekends

[Trello Card](https://trello.com/c/HEihTyLf/57-weekend-schedule-don-t-display-times)

Students can choose to spread out the work over Sat/Sun as they please.

start_time will still be specified to facilitate ordering. The estimated duration should be displayed in it's place instead
I would use a helper here. Also, should use `params[:number]` directly and instead use the helper method `day` (found in `CourseCalendar` concern) to access the day. Not only is this cleaner but also less coupled to the `params`. Also b/c `params[:number]` can be `"today"` in which case I don't think this will work. Whereas `day` helper is going to return `"w2e"` instead.