Multimedia Support in Vellum

![screen shot 2013-06-03 at 3 59 29 pm](https://f.cloud.github.com/assets/716573/601748/2ee6ac96-cc88-11e2-90db-f643532af4eb.png)

Related:
https://github.com/dimagi/commcare-hq/pull/398
https://github.com/dimagi/hqstyle-src/pull/39