Bug 5106 - allow embeds from kickstarter fundraising widget

Kickstarter has multiple widgets which we want to allow embedding for. Bug 4852 allowed www.kickstarter.com/*/widget/video.html, but we also want to enable card.html, and other widgets that Kickstarter may create in the future.

Also add a new test URL based on a modification of the URL added in bug 4852.
Merge pull request #572 from stormerider/bug-5106

Bug 5106 - allow embeds from kickstarter fundraising widget