* Add information on who started flow on a node with name where possible.
Add sealed class holding information on different ways of starting a flow: RPC, peer, shell, scheduled.
* Remove invokeFlowAsync from ServiceHub, move it to ServiceHubInternal.
We shouldn't be able to start new state machines from inside flows.
* Remove progress Observable from FlowHandle, unless explicitly requested.
* Refactor FlowHandle creation into FlowStateMachine.
* Prevent server-side queue subscription for dummy Observable.
* Refactor so that RPC client does not receive any unused progress Observables. This is the simplest way of ensuring we have no dangling "hot" Observables when the RPC client closes.
* Test flow has correct handle.
* Resolve some compiler warnings.
* Document how starting a flow does not involve progress tracking by default.
* Update changelog and release notes for RPC API.
* Rename new RPC API to startTrackedFlow().
* Remove optimisation because of its affect on the client-side.
* Update documentation.
Standaridise the identity names of Alice, Bob and Charlie, notary, map service, etc. in order
to ensure consistency across the code base and reduce number of places that have to be changed
to introduce proper X.500 names.
Move Alice, Bob & Charlie identities into the utilities package so they can be used in demos
