Logo uploader

requires https://github.com/dimagi/MediaUploader/pull/5

Adds uploader for CommCare logos in Java and Android.  Currently behind a feature flag while the kinks are ironed out.

![screen shot 2014-12-17 at 6 11 11 pm](https://cloud.githubusercontent.com/assets/1757035/5480836/2658684e-8618-11e4-8a53-dc2010691241.png)
![screen shot 2014-12-17 at 6 11 26 pm](https://cloud.githubusercontent.com/assets/1757035/5480839/29a2c2d8-8618-11e4-9aa1-e6811f15b201.png)

Known issues:
- on staging, YUI does not get applied to the "Select File" button
- integration with mobile needs to be completed
- recommend usability improvements before we expect end users to navigate this feature (similar to menu/form multimedia uploader)

@biyeun 
since this is a refactoring of existing code, I'm going to recommend handling it in a separate PR once this one is on master