Setup backbone model & collection for tags
Add tagging collection/model & parse taggings

Notes has an association to taggings that is parsed into the note model
in backbone.
Add swapping router helper

This is copypasta from ThoughtBot's backbone on rails book. It extends
Backbone's routers to have a swap method that handles garbage collection
when switching between views.
Bootstrap initial data set into backbone
Install backbone-support gem

This replaces the swapping router work committed earlier. The gem
provides a number of utility classes and methods from thoughtbot that
help with backbone garbage collection.
Render notebooks index

This is pretty hacky right now, but I wanted to get something on the
page as a starting point. Long run goal is to refactor this into
something that uses composite views and therefore doesn't require me to
overwrite backbone-support's swap function.
Render tags index in backbone
Use top level backbone variables

No need to pass notebooks, tags, etc down through the routers and views,
since they are defined at the top under Nevernote.#{varname}
Render notes index in backbone
Rerender notes list on change of notebook or tag

Again, super hacky implementation that needs some
rethinking/refactoring.