Split REST services out into a separate plugin

As you can see, the bulk of this work is moving files into a different child project, which means no package (or other) changes. Beyond that:

* The security service cannot depend (straightforwardly) on J2EE classes, so a contract needs to change a little. Its IT needs to be split in two: one to test Postgres access and one to test REST access.
* Maven's ant plugin is used to copy plugin files into the local plugins directory. I'm happy to make this target/plugins, if that seems better. This supports both developers running and staging for packaging.
* The name of the new plugin is `rest`. Another possible name would be `http`. I could have made two plugins: HTTP and REST, but didn't see an overwhelming need. It's not hard if anyone else does.
* Some documented (mostly newly documented) config properties changed. From `fdbsql.{http,rest}` to `plugins.rest`. If we did split into two plugins, I could be talked into making the plugins prefix `fdbsql`. Of course, that's a possible conflict with core properties, but I'm not sure this is a real-life concern.