Display property implementation status on sidebar

Display the implementation status of properties on the HSS doc.
sidebar.

- Implemented: The property either has no values or all it's values
  have a version number set.
- Semi-implemented: One or more values don't have a version set
- Non-implemented: No values have a version set

Currently future versions are also considered to be valid versions.
This means that a property that has some values with future versions
could still be considered to be fully implemented.

Close #462