Make 'isInferred' a Local Thing method

## Problem to Solve

Workbase is slowed down by a large number of roundtrips to retrieve the `inferred` flag on Things

## Current Workaround

It's slow

## Proposed Solution

Make `isInferred` a Local Thing method

## Additional Information

It was local in 1.8 but was made remote to reduce payload size and simplify the protocol. However 1 bit is an acceptable cost.