Indicator selector data origin view uses Backbone as an event bus

This is because Backbone Diorama has a bug that removes event handlers
from cached sub views when re-rendering ($.remove() also unbinds event
handlers when removing the element from the DOM)
Selecting from a fancy select correctly changes the selected status on
the original dropdown
Toggle clear search button in indicator selector when no search term is
entered
Move the FancySelect to a Backbone View

We unfortunately have to maintain a changing state inside the DOM (the
currently selected list item), which requires re-rendering a template.
It's easier to do this with a backbone view than try and hack it
together.