[FEATURE] Include plugin version in seralization state

[Steven Atkinson]

As a way to smooth out forward compatibility, the plugin's current version can be serialized in the state. This way, if/when details of its serialization are changed (e.g. names/ordering/existence of parameters, e.g. #385), this can make updating the plugin less hazardous to projects and the like that are currently being worked on.

This will enable all sorts of other features to be much easier to accept :)