New componentized version of explore/explore-collection header

It allows you to set the title,button classes and names, and the type of button
toggle, radio or checkbox.  It defaults to checkbox.  It also handles the
button toggle and search user interaction events.

When the user triggers a search by clicking the search button or by typing in
the search field, the component handles aborting the form submission and
toggling the clear search button.  It then triggers a 'search' event on the
component.  This event is debounced to 666ms so it only triggers after the user
stops typing.

The component also watches click events on the buttons, triggering toggle
events on itself when the click results in a button state change.  There is a
'toggle' event when any button state changes, containing an array of hashes,
each hash pairs the class name of the button with its new state.  The component
also triggers individual 'toggle:[class name]' events for each change.
Merge branch 'master' into 177-header-redesign
added readme for new component
updated readme
added search clear
Added center text and adjusted spans
size / positioning style for header component
remove title
permanently stick header to top
have explore page attach header component instead of rendering directly
deregister toggle event on undelegate events to prevent multiples
included bootstrap-button
change self to this now that triggerToggle is a method
bind and defer triggerToggle so that it is invoked with the proper this after the active state update
change explore page to search and filter with the new component events
disable showing banner
added some filters buttons helper methods
better activeButtons method
oops, class is reserved
update filter buttons toggle on load