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.


As things stand right now, after I made things consistent, there is no top-level (services-config.yaml) requirement for plugin services. They are required by the resource inside the plugin, as here.

This means that there is no way to disable plugin services other than deleting the plugin.

Conversely, if plugin services were included in services-config.yaml, then if the plugin were not present, there would be a startup error. Would that be better? I suppose it's easy enough the edit the file if you delete the plugin.

Or should we have a `require-if-bound` clause in services-config.yaml for standard plugin services. This could hide typos, but again might be okay for the standard distribution.