Adding functionality for embedding:

* Added button to display embed code in collapsible text. Text is selected so user can copy when it displays
* Added url rule for embed versions of the url
* Split base.html so that display.html and embed.html extend it as necessary
* Embedded html looks exactly like display html, it should be modified for size, etc.
Merge branch 'master' into embed

Changes to deal with single-variable forms
embed style added
embedding uploaded to appengine