Updating the ORA project and description on the edx code front page

Updating the index.html for our open source project, so we advertise our new ORA project, rather than the old.

@nedbat just a quick glance if you could, to make sure this is reasonable
@srpearce @Lyla-Fischer I'm not really happy with my new description (but did not like the old one much) I wanted to get your opinion
Also @wedaly  
"new" will be out of date soon, and I'm not sure "is an XBlock" is the most interesting thing.