added the passport auth for the post operation

the passport.js module will take care of a session
changed the callback of github.

[fixed #48]
changed the GitHubStrategy

the Github strategy was wrong -> was calling the localhost
Removed the github auth url redirect from api server.

The github callback url will be setup in the github service settings.
Added a collaborator check for post operations

using a the Github API we make sure that a post to the database is a
collaborator of the repo

[fixed #50]