Simplify the concept of a "campaign" in the metadata

[dostuffthatmatters]

• no longer have "default locations"
• just have a list of locations and sensors associated with this campaign
• the merged output files will not have constant column names but species_sensorid_locationid_unit
• by this, the exported files need to be parsed a little bit more, but still "same column name = same sensor and location"
• This makes the "campaign" definition and export much more flexible!