Bug 1023662 - [User story] Show 5 day week view r=gaye

**WIP**, still going to clean up the code and try to use external templates for most of the elements.. I have a few more changes locally (trying to abstract it better so that we can use same logic for day view as well), but will probably take another full day to clean up the code..

I'll rebase this later and squash commits.
I think this is OK, it's way less lines of code than writing a `toArray`.. I tested with the a bunch of busytimes (heavy workload) and performance was OK, so I think it's unnecessary to improve the performance for now..

in the future I would like to remove the IntervalTree and use a simpler cache based on days... but too much work for now.