Began adding IBIS support (process/issue/option/argument nodes).

Serialization/deserialization not supported at this point.

Readme not up to date.

Issues and arguments should have some extra properties, which don't have
any new UI at this point.
Added Open/Settled indicator to issues.
Stopped making multiple circles elements for junctions.
Added refutes/supports to arguments.
Coloured in nodes of different types.