Add support for REST service POST requests.

This is working with an Inventory adjustment. For example, POSTing this:
```
https://example.com/your-db-name-here/api/v1alpha1/inventory/adjustment?access_token=12121212121-asdf-asdf-23232323232323&quantity=12&itemSite=4fceab32-d1c0-4465-d0af-e2b5b081058f
```

Note, I'm not sure how some of these "options" query parameters are going to work. I talked with John about this and he may be tweaking those a little. See TODO here:
https://github.com/bendiy/xtuple/blob/68683c70b45637bc9e5356d8a2f64ad0cc686f82/node-datasource/routes/restRouter.js#L307-L309