Rename Frontend References of 'Sensor' to 'Method'

[daniel-slaugh]

HydroServer extends the SensorThings Sensor table to be more general. It can define either the physical instrument deployment that's producing data or the method by which a group of data came to be including derivations/calculated values or human observation.

The name Sensor doesn't communicate well the more general case, so we should consider renaming all user facing references of Sensor to Method. In order to stay compliant with the SensorThings specification, we should keep the Sensors database table and references to Sensor in the API.