Using hashed lat/long for BNA's source_id leads to error

[stefanpernpaintner]

Currently the source_id value for BNA's charging stations is filled with the has value over lat/long. This leads to the situation that some charging stations have the same hash value because they have the same lat/long values set (most likely by error) and this in turn leads to the fact that some stations cannot be imported because of a unique key constraint error (source_id has to be unique)

I think we should generate the hash over all attributes of the BNA's charging station to avoid the described situation

[mjmader]

Actually the problem is that the rows of the BNA data (and also FR data btw) have changed over time to resemble charge points of charging stations, rather than just a charging station per row.
In effect, we have to do some preprocessing to flatten serveral charge points into a single station.
On the other hand, this is also important for #28, maybe it is better to change our schema to actually handle charge points