Lockable

[spengrah]

This PR makes HSG lockable so that the owner can prevent any further changes to parameters and settings.

• closes #40
• adds a SetupParams struct to the initializer instead of arbitrary bytes

Locking will incorporate the following owner authorities:

• setOwnerHat
• lock
• setMinThreshold
• setTargetThreshold
• addSignerHats

The above will likely later also include...

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