Improve Service compatibility check

[kurtkilpela]

Service compatibility is current defined as having an equal number of instance variables and a matching template. This isn't sufficient as the names of the variables may have changed or they may have been reorganized.

Instead, we should hash the variable name sequence and include that in the message when serializing a service. The hash should be checked while reifying services. If the check fails, this incompatibility should be reported.

Suggested name of exception: ServiceIncompatibility