Feature/auth service integration

Integration of COOPR server and External Authentication service from CDAP project. As was discussed before with @sreevatsanraman , I used dependency to the cdap repo, but in future it should be replaced with dependency to the common repo. 
Also, I copied class ```SecurityAuthenticationHttpHandler``` from the ```cdap-gateway``` package. This class also could be reused, so @sreevatsanraman , could you please move this class to the common auth service too? Then we could delete it from this repo. 
@albertshau , please take to review this PR.

this is not great either, but I see the ExternalAuthenticationServerTest does the same thing... so I guess it's fine to have this here for now.