Merge pull request #101 from mfairchild365/embed

Let mediahub manage embedded markup
Merge pull request #102 from mfairchild365/embed

Version 2 Embed code updates
Add a poster field to the media table
Add the poster field to the media form
use the custom poster image if it is not empty
Make help text medium agnostic

Could be for audio or video
Explain how the poster image will work

It will override the custom one chosen
Add container divs

This will make it easier to let JS manipulate
Hide/show the poster picker
Don't auto play on the add media view
Make sure that the key is set
Still show the image, just hide the button
Show the default poster when switching
Add a script to remove 404 posters