"add event" hide/display, addition of "cancel" button

[dorono]

• got add event button hiding and displaying when on /add-event route
• updated tests to verify button hide/display behavior
• added cancel button to add events page, takes user back to home page/event list

iPhone simulator view

[pdw207]

Maybe we should have a max width on the form. Doesn't necessarily need to be in this PR.

[pdw207]

Eventually we can put this in a modal and save the state with the add-event url.

[dorono]

@pfarnach Totally agree about putting the routes into constants, much cleaner. As for the max-width, I do indeed see one on line 5 of src/components/AddEvent/AddEvent.sass:

  max-width: $max-width
  margin: 0 auto
  padding: $base-spacing

I also see that the width of the form matches the width of the header looking at the site in the browser. Or am I maybe understanding?

At any rate, gotta hit the sack for an early trip out of town tomorrow, but if it looks good to you otherwise, my vote is to merge to keep it from getting stale.