World-wide flood detection test, JSON from MatsuAnalysis, and GeoPictureSerializer memory leak

Several recent improvements:

    (1) World-wide flood detection test (https://github.com/jpivarski/matsu-project/commit/3bbe7bfb1ee7c67ea965f3d45688f8a21075c62b#mapreduce/modules/flood_detection.py): one-line correction in flood_detection.py, configured shell scripts for running flood-detection over the whole world.

    (2) JSON from MatsuAnalysis (https://github.com/jpivarski/matsu-project/commit/202a5d2ff40d549dadbb490ca0a6e5828f6cac8f#lib/serialization-avro-java/WebContent): added the ability to extract a JSON file of pixels from MatsuAnalysis to provide a mostly GUI-based way of building training datasets for flood-detection.

    (3) GeoPictureSerializer memory leak (https://github.com/jpivarski/matsu-project/commit/f6a2b0e3e2ee098994ca2d2ecba04edbd0e49ec1#lib/serialization-avro-python): the C-based object had no dealloc function.  Turning .picture into a property (with explicit getter and setter) was used to diagnose the problem, and it doesn't hurt to leave it as it as a property.