Only add setDragImage if the browser supports it

Fixes #464
Merge pull request #463 from arv/form-data

Add FormData wrapper
Merge pull request #465 from arv/set-drag-image

Only add setDragImage if the browser supports it
Update CONTRIBUTING.md
Add support for reflecting the hidden attribute
Merge pull request #469 from arv/hidden-property

Add support for reflecting the hidden attribute
Wrap window getDefaultComputedStyle

getDefaultComputedStyle is a Mozilla proprietary extension but
jQuery uses it so we have no choice but to support it.

Fixes https://github.com/Polymer/platform-dev/issues/32
Add wrap examples
wrap example should use properties
Merge pull request #472 from robdodson/wrap-examples

Add wrap examples
Disable eval for Firefox OS Apps

Fixes #467
Merge pull request #473 from arv/firefox-os-apps-disable-eval

Disable eval for Firefox OS Apps
Filter wrapped NodeList contents from native NodeLists

Fixes #629
Merge pull request #474 from MediaMath/nativeQuery

Implement newly proposed DOM selection approach
Handle native querySelector returning nothing

	- Fixes #476
	- Added tests
Merge pull request #477 from MediaMath/nativeQuery

Handle native querySelector returning nothing
Account for DOM selection in sub-shadow elements

	- Fixes #480
Update README.md
Merge pull request #470 from arv/get-default-computed-style

Wrap window getDefaultComputedStyle
unwrap(FormData) fails