1st pass at determining window #3914

The window start and end dates for an event
implement event window computation and tests #3914

This has to work around the mother incorrectly being associated with
child events. The only case not handled is when multiple children
exist with different birthdays. It will arbitrarily pick a birthday to
use as the window offset.
UI for event windows #3914

The UI of the 'Participant Schedule' tab needed to be reworked to
include windows. Activities are now further seperated by Event within
a given scheduled date so that a relevant window can be displayed.

Conflicts:
	app/views/people/_events_and_contacts.html.haml
	features/support/fakeweb.rb
Merge pull request #159 from NUBIC/feature_3914_event_windows

Feature 3914 event windows