web,admin: add instance simulations

[Bogdanp]

This doesn't actually work as-is since the sandbox blocks cookies altogether rather than using a separate cookie jar per iframe.

[MarcKaufmann]

But can it be made to work, or will it be too time-consuming?

[Bogdanp]

Probably the only way to make it work using this approach is to use that Chrome-only iframe feature. Otherwise, I think it's going to be too much work.

Too much work idea: session ids in query params.

Different idea: call run study form "simulation" continuations with the right parameterizations for user and current participant.

[Bogdanp]

The simulate command works as we discussed during today's session, but there's some sort of bug during teardown that I need to investigate next session.