Tidy up documentation of the "Submit (On Behalf Of)" permission

The documentation refers to "SubmitAs", but the permission is actually
named "Submit (On Behalf Of).  Update the documentation to refer to the
correct name.

Move the documentation of the permission to its own section, rather
than only mentioning it inside the "Submit" section.

Change-Id: I9c8deb3506a72ca614e6419157d5b1bed594e176
2 files changed