Create endpoint for granting read/write access

[dolsysmith]

Implement initially as a separate endpoint/view: this will facilitate development and testing, if we don't want to ask for the expanded scope from everyone by default.

[dolsysmith]

Easiest approach is probably to accept an optional parameter parameter to the base root (e.g,, &/activities/update), in which case we append to the /read-limited scope string when creating the redirect for the SSO process.