Make all scala rich stubs have apply method instead of specific name

Before, MapStub required the user to specify a map() method, now they
specify an apply() method. This is more in line with how Function1[] and
so one works and also the same across all operators.
Add deferred updates to workset iterations (issue #21) and fix chaining of iteration state updates (issue #123)
Formatting and minor cleanups in iteration code.
remove discoveryManager
yarn now also starts the web interface
extended pact-client to nicely support remote execution.
unified 'run' and 'remote' in pact-client
Fix issue of selecting wrong class loader in combiners.