Support data import via Avro

[kenwenzel]

The Avro file format is a compact binary format for transferring data:
https://avro.apache.org/

We should consider adding Avro support als alternative to JSON and CSV at least for importing of data.
In its simplest case a scheme with a flat structured record of scalar values could be used:

{"namespace": "lf.avro",
 "type": "record",
 "name": "data",
 "fields": [
     {"name": "time", "type": "long"},
     {"name": "colum1",  "type": ["string", "null"]},
     {"name": "colum2", "type": "double"}
 ]
}