PhantomJS ci fixes

Address issue #5

I hope you don't mind me reverting the Firefox changes. The commits seemed to indicate a fruitless effort :frowning: 

I just had to do a couple things for compatibility in PhantomJS. For instance, dom elements didn't have a remove() method. I had to use  `angular.element(placeholder).remove()` which might be a better practice anyway.

The more serious problem was lack of support for video. So I just mocked it out with `jasmine.createSpy`. I think it's ok, at least for now. I could add some `FIXME` comments to drive home that it should be dealt with at some point. But the tests are at least [passing on travis](https://travis-ci.org/bmatsuo/webcam-directive/builds/16798059)