Minor updates to `peterlloydcc` work to expose the ability to
override LDAP membership via the API. This along with `peterlloydcc`
original commit allow users to set the override flag on a member
to true or false, as needed.

Previously, setting access_level for LDAP users was not allowed.
The web interface is able to set an 'override' attribute to stop
LDAP sync from changing the access_level. This adds the same
ability to the API.

Also update API documentation and add tests