CDAP-503: Removed dependency on the cdap project.

This PR covers following cases from the jira [CDAP-503](https://issues.cask.co/browse/CDAP-503): 
b) Remove dependency on Constants class by hardcoding gateway version in AbstractAuthenticationClient.java

c) CDAP-clients then depend on artifacts from common repo and removing the dependency artifacts from CDAP repo

@sreevatsanraman , please, take a look or delegate this to the responsible person.