Use embedded-mode in Derby acceptance tests

- [x] Added EmbeddedDerby test fixture
- [x] Converted Derby acceptance tests to embedded mode
- [x] Using in-memory db (avoids polluting file system with db files)
- [x] Converted JUnit invoker of Derby acceptance tests to annotated ones using FitNesseSute. Removed JUnitHelper dependencies. (This helps for #179)
- [x] Bumped up Derby dependencies to latest stable version
- [x] Remove derbynet.jar dependency

Closes #217 since network mode is not necessary any more.