Initializing a bridge deletes the database

[Paula-Kli]

For sensors and actuators the database gets deleted when initializing a bridge with an id that was seen before. In that way we do not risk assosiziating non existing sensors with a bridge which might have different and new sensors and actuators.

At the moment the sensorfeeds do not get deleted by cascade which might be good to store the data for later or bad since we do not know which datatype the values have if we delete the assoziated sensor value in the database. But the bridge will initialize all the sensor again anyways.
(it also prevents us from overflowing and getting ids higher than 253 after initializing the same bridge several times see also #14

[Paula-Kli]

Update from 6a94887 :
we delete the sensorfeeds since postgresql does not allow them to stay but it happens manually and not by the database cascade