Make it possible to change the RPC end-point

[jonasbjurel]

Is your feature request related to a problem? Please describe.
Today the RPC endpoint is fixed to 127.0.0.1, I.e JMRI and MyRailIO needs to run on the same host.
It is proposed to be able to provision this endpoint (address and port-base) such that JMRI and MyRailIO can run on separate hosts.

Describe the solution you'd like
One alternative is to provision the end-point through a JMRI memory variable.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.