Client Thread creation refactor

Created by: SmithRWORNL

Currently, the Client's processItem function is creating and running a thread while having no way to synchronize with it. This is causing build failures in ClientTester (part of Issue #176 (closed) ). Alex and I discussed the problem, and propose that Client be refactored to take a thread creation factory. In real cases, this new factory class will function identically to Client's current code, but it will allow us to inject a fake thread factory which does not actually launch any new threads for use with test classes.

Since this plan would modify a core part of ICE's API, we thought it would be best to open an issue for discussion on how to deal with this test failure.