Grab bag of fixes and usability improvements resulting from demo app development:

Grab bag of fixes and usability improvements resulting from demo app development:

* enyo.Collection
	* Add `isFetching` property, for showing loader spnner via binding
	* Merge destroyAllLocal improvements from master
* sources/xhr.js
	* Separate jsonp and ajax request options, so callbackName can be passed
* enyo.Image, ui.css
	* Add `sizing` property, which renders image as `<div>` with background-image, and allows use of `contain` or `cover` background-size properties
	* Add `position` property for use with `sizing` property, for setting background-position
* enyo.Media
	* Make `duration` and `currentTime` bindable
* enyo.DataRepeater
	* Fix error thrown when removing currently selected item in DataRepeater

Enyo-DCO-1.1-Signed-Off-By: Kevin Schaaf (kevin.schaaf@lge.com)