Implement: PUT add specified property to all entities

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Migrated from Gitlab issue 7

• HTTP method: PUT (new code called from function handle_put())
• Operation: AddProperty
• Parameters: Table name
• Body: JSON object with a single name / value pair. This name * value pair will be added as a property to every entity in the specified table. If an entity already has that property, whatever value it has already will be replaced by the value provided in this object.
• Response codes:
  • status_codes::BadRequest (400): Missing table name, missing JSON body
  • status_codes::NotFound (404): Table does not exist
  • status_codes::OK (200): Table found and all entities extended with the specified name/value property