Fix the scope for `prependChildTo`

Similar to 589866de63f, prepending elements to another element in
a composite view, should not prepend to all the selectors that match
in the document.
Update backbone-support/support.js

Update variable declaration to comply with strict mode ("use strict").
Also backwards compatible for non-strict mode.
Update docs for Support.Observer
Add 'swapped' method / event to composite_view

Allows for triggering events when the new view is added to the DOM

- SwappingRouter calls the swapped method if it exists
- CompositeView emits 'swapped' event

Closes pull request #11 - 'Add a call when the view has been swapped'
Move backbone and underscore for asset pipeline

- Move jQuery into the spec/ folder as we want to use the version
  bundled with Rails
- Provide Backbone at Underscore via asset pipeline
- Update README to reference included versions as well as how to override