[demo] Validate the contracts when they are given by address

[juharris]

Currently an error is shown if something fails when loading the contract but it would be better to get more detailed errors for what is invalid.
Validate that:

• Address is for a contract.
• Components (model, data handler, IM) exist
• The component contracts are owned by the main entry point.

Leaving this issue open since there's probably more to validate.