Github readme intergration

This adds the ability to embed an image into a github README.md file.
The assumption is that there already exists a widget in cloudify with the given ID.

The markdown looks something like this: 
`[![Launch with Cloudify](http://localhost:9000/embed/img/ab0cb11a-8030-48f7-b3b5-94bd0b68336b)](http://localhost:9000/widget/single/ab0cb11a-8030-48f7-b3b5-94bd0b68336b)` (or course, replace localhost with the appropriate host name).

Here's more or less how this looks http://cl.ly/image/2j422H0e3t2m Of course the actual image graphic needs to be improved...