WS-797: Polishing QA process

Changes

Back-end

• Added new determine_state method to CapabilityRequest that will determine request state automatically, based on the state of its versions
• Capability execution state transitions now occur before the action is performed, so effectively the action is performed from the next state

UI

• "Submit" button now appears based on the state of the selected version rather than the state of the request
• The request's latest version is now selected by default in the dropdown
• Removed extraneous QA-pass button

Completes WS-798 and WS-801