- Also renamed "frequency" column to "interval", can be used for all sensors

Add SensorConfig::loadCache() that loads all published sensors into a list and creates a map for faster lookup of sensor names

Introduced a bit mask for sensor properties in dcdblib and dcdbconfig (e.g., integrable, monotonic,...)

Still pending: honor scaling_factor during query().

* Extended DCDBConfig and SensorDataStore to provide functions for querying data
* Adapted dcdbquery accordingly
* Project now compiles again but dcdbquery likely to be broken

* Added SensorConfig and DCDBPublicSensor classes as interface for dcdbconfig
* Fixed bugs and tested:
  --> CollectAgent fully working
  --> dcdbconfig fully working