change Guice modules used in server tests to Gin modules (and wrap in adapters on server), so that they can be used in client tests
begin refactoring client-server communication for testability: introduce injectable ServerRpc interface to handle HTTP communication, factor login logic out of servlet and call directly from test implementation of ServerRpc
big refactor to support client testing; add tests for login widget
Merge pull request #61 from kprevas/master

initial work on tests for client code