Added casPassThrough. By default false, in case this set to true it will
pass the request through the filter chain instead of issuing a redirect.
This is make cas proxy authentication work when cas proxying is
initiated from a java client application.

As the ClientFilter is more generic (i.e. used for authentication
mechanisms than Cas) probably a tighter check is required. One approach
may be to check for presense of CasProxyProfile in the
principalCollction but would require a dependency on pac4j-cas which is
not there at present.
Changed the name of casPassthrough property to
redirectAfterSuccessfulAuthentication (default true). Added javadocs for
the property.
Changed default value of redirectAfterSuccessfulAuthentication to true.
Merge pull request #7 from dinabandhu/master

Added casPassThrough. By default false, in case this set to true it will