cmgr should validate picoctf required params

[dbrumley]

The author attribute and the point config needs to be present in problems for the picoctf platform, but cmgr raises no warnings when not present.

[dmartin]

In theory cmgr could be used by multiple consuming clients, not just the picoCTF platform, so I have avoided hardcoding anything pico-specific so far.
But as we are probably the only actual existing client application, I agree these would be fine to add (at least as nonfatal warnings).