Governor module for governance-settable parameters

[frangio]

Governor parameters are set via overrides: votingDelay, votingPeriod, proposalThreshold. I think we should have a module that keeps them in storage and offers an interface to update them via governance. (Note: The quorum module already works like this.)

In Wizard, I think this would look like a toggle like "Updateable parameters" that switches between defining pure overrides and inheriting the module we provide.