Upgradeto latest yasnippet

Hi,

I have updated the yasnippet extension to the latest version. This needed to be done because I need the latest version capabilities for my JS development and I also need the epy setup.
Changes:
1. Added yasnippet as a git submodule pointing to https://github.com/capitaomorte/yasnippet. So future updates will be trivial
2. Changes the epy-editing to remove deprecated calls yas and use the newer api.
Testing:
The change is pretty trivial and should not affect anything.
I have tested it on my local setup and it seems to be working fine. Since there are no automated tests, you might need to do a sanity check to make sure I haven't broken anything