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#find` and `View#findAll` as great shortcuts for `querySelector` / `querySelectorAll().toArray()`. I'm using these names because these are native methods on `Element` since [this spec](http://www.w3.org/TR/selectors-api2/#interface-definitions) and because they are short and concise.
* `utils.delegate` and `utils.undelegate` for native event delegation.
* `utils.matchesSelector` and `utils.ajax` for fast and convenient minimal selector matching / XHR shortcut.
* `Backbone.Deferred` for custom deferred libraries (I think this is a big deal since Chrome now has native promises, other browsers will soon have too)
* `View#useNative` property if you still want to include jQuery but also want to use native methods for some particular views (hot code)

Behaviour in no-jquery env:

* No `View#$el`.
* No custom jQuery features like selectors (`:first`) and [event namespaces](http://api.jquery.com/event.namespace/) (`click.ns`), I think it's pretty obvious — if you want them, use jQ. Ordinary event delegation and bubbling works just like before.

Native DOM view tests are in `test/no-jq.html` and `test/view-no-jq.js`.