Custom error handling for: attempt to index global 'grpc' (a nil value)

[rkusa]

The most common error I see support requests for is:

attempt to index global 'grpc' (a nil value)

I'd thus suggest that we add a manual check for whether grpc is defined and if not, stop everything else from running and print out a more helpful error message. Something in the lines of check your MissionScripting.lua.

[rkusa]

• If grpc is defined, check that the expected methods exist, and if not, print out all available fields to help debug the cause (see attempt to call field 'simulationFrame' (a nil value) #215)