Introduces the following new metadata fields:
- frequency
- tle
- location (latitude, longitude, altitude)

These fields are addded as serialized using json in a new HDF5Field called
"metadata". It includes all metadata about the associated observation,
thus the observation id is moved from its own HDF5Field into this metadata
section.
Signed-off-by: Fabian P. Schmidt <kerel@mailbox.org>