Add AuthenticationHandler that uses Kerberos but allows for an alternate form of authentication for browsers

It would be useful for some Oozie users if, when using Kerberos, that browser access to the oozie web UI could be authenticated in a different way (w/o Kerberos). This may be useful for other projects using Hadoop-Auth, so this feature is to add a new AuthenticationHandler that uses Kerberos by default, unless a browser (user-agents are configurable) is used, in which case some other form of authentication can be used.