Make use of methods / properties in Python more consistent

[james-whiteside]

Problem to Solve

Recently, the Python driver was updated to replace many methods with properties, for example:

Transaction.query()

became:

Transaction.query

This change was not propagated to all parts of the API, for instance:

Explanation.condition()
ConceptMap.explainables()

should probably be:

Explanation.condition
ConceptMap.explainables

but are currently not. This inconsistency makes the API difficult to work with.

Proposed Solution

Update all existing methods to properties wherever appropriate.