Remove jQuery dependency.

As discussed in gh-2859, taken from [Exoskeleton](http://exosjs.com).

This change makes jQuery dependency 100% optional.

If jQuery is included, everything will still work as-is.

New stuff:

* `View#delegate` and `View#undelegate` for native event delegation.
* `utils.matchesSelector` and `utils.ajax` for fast and convenient selector matching / XHR shortcut
* `Backbone.Deferred` for custom deferred libraries (I think this is a big deal since Chrome now has native promises)

Native DOM view tests are in test/no-jq.html and test/view-no-jq.js.