Bug 1071919 - [Calendar] Settings drawer can become stuck open requiring app to be force closed r=gaye

bug caused by race condition, that's why it's intermittent and not so easy to reproduce...

I was not able to write a marionette test to catch this regression (bug did not reproduce on marionette tests), so I think we will need to land it without tests.

code is basically triggering `_onDrawerTransitionEnd` before the class was added to the body, so it was behaving as if the user was closing the drawer, which made the view to get into a bad state (after opening the drawer again it did not have the click events).