Several changes:

* Rework (again) the servlet dir hierarchy
  - Now we call them "engines" (not servlets)
  - App knows about engine types
  - Engines expose a loader file, which knows where the
    files for that engine are located, and loads them.
* System engine follows traditional app hierarchy (rails?)
* Rework test dir hierarchy to reflect this change.
* Added rspec helper to create in-memory db for model tests
* Added fqdn model unit tests