[v0.5] Ability to query states

[markzyu]

• Able to query state of a ReadOnlyChain (is it stopped? did it end in error?)
• Able to forcibly stop execution of a specified ReadOnlyChain
• Able to query whether all chains produced by a specified ActionChainFactory have finished execution (either successful or with exceptions).

Going to do this in branch "b0.5"