Adding nginx role

* New role for nginx, main.yml will install the nginx package
* By default create the basic version nginx config
* Add variables for nginx package version and template in group_vars/all
* Refresh apt-cache in common role
creates basic nginx configuration, default and lms, adds nginx handler
re-add lms
adding lms-backend
Merge pull request #2 from edx/jarv/nginx

Adding nginx role