ability to inject plans / objects into the worker

[tacaswell]

If we trust the users they should be able to inject into the server new plans (and objects?) similar to how they do they do now when they are at the beamline. This needs to be done carefully as it is letting the users send us arbitrary Python code. We should consider

• details of the mechanism (eval/exec, write to disk and import)
• how to persist user added plans + devices
• should we bother trying to validate / sanitize / sandbox (S. Dower has publicly said this is a lost cause)
• if there needs to be any review steps by BL staff before the code is accepted to the system