Allow specifying subject and session IDs for single-session case

[garrettmflynn]

fix #689

[bendichter]

The error messages are showing up twice for me on page load. I would really rather they don't show up at all until I hit submit.

[bendichter]

I also get taken to this page, which should not be reachable in single-session mode

[garrettmflynn]

Alright this should be good to review now

[bendichter]

Now for some reason it is not letting me specify Age instead of DOB

[garrettmflynn]

Good catch, thanks! DOB and Age use an alternative mechanism to handle requirement status (i.e. conditional requirements), so these properties had to be excluded from the recent changes.

[garrettmflynn]

@bendichter This should be good to go!

[CodyCBakerPhD]

@garrettmflynn Failings tests for this PR

[garrettmflynn]

Thanks for the ping. Fixed

[bendichter]

LGTM!