Initial "getting started" documentation

- Cover the welcome screen, initial "settings" screen, "APIs" screen, "Create
New API" dialog, "API
 Overview" screen, "RPC Services" screen, "New RPC Service" dialog, various
views and edit screens
 in an RPC service, and initial testing of a service.

TODO
----

- [x] Create a REST service
  - ~~Cover REST terminology~~
    - ~~Entity~~
    - ~~Collection~~
    - ~~Resource~~
    - ~~Link relations (pass them to the halprimer for details)~~
  - ~~Fields~~
    - ~~Required~~
    - ~~Filters~~
    - ~~Validators~~
  - ~~Documentation~~
    - ~Collection vs Entity~~
    - ~~Multiple methods~~
    - ~~Collection response~~
    - ~~Entity response~~
    - ~~POST/PATCH request~~
  - ~~Authorization~~
    - ~~Show creating rules~~
    - ~~Show adding Basic auth~~
  - ~~Sample resource~~
    - ~~**Need to find some way of demonstrating without needing a database!**~~
- [x] Test the service
  - ~~POST without credentials~~
  - ~~POST with credentials~~
  - ~~POST with invalid data~~
  - ~~GET with and without credentials~~
  - ~~PATCH with credentials~~
- [x] Documentation
  - Show link from landing page
  - ~~Show link in navbar~~
  - ~~Show documentation landing page~~
  - ~~Show API landing page~~
  - ~~Show expanded service~~