Definition of the version field in OneKey data structures & change type to a positive byte data type

[jwrosewell]

The documentation contains multiple definitions for the "version" field of the signature.

Identity Response - "The type of contracting party in the PAF ecosystem"
Identifier and preferences - "A version number made of a "major" and a "minor" version numbers. To be detailed."

Now that we're approaching live deployments the meaning of the version field is becoming more important and should be defined consistently across the data model. It should reference a version of this documentation which describes the fields and how they are populated and used. It should not relate to any other considerations.

This is also an opportunity to optimise the data model by using a single positive byte between 1 and 255 to represent the version.

Where the data is stored as JSON there will be no impact to the number of bytes consumed. "0.1" uses three bytes. 255, the largest version available, would also use 3 bytes. Where the data is stored as a byte array then 1 byte will be needed compared to 4 bytes for the equivalent string encoding. When considering data consumption and overall performance, and the number of times this field will appear in transactions the saving could be significant.