Update train-cloud-microphysics demo app for merged ICAR files

[rouson]

With this PR, putting the latest ICAR NetCDF training data files in a subdirectory demo/fiats-training-data and running something like

cd demo
./setup.sh
ln -s `find build -name train-cloud-microphysics`
./train.sh

should launch a run that does successively refined training of a cloud microphysics model by conditionally sampling the training data to flatten the output-tensor histograms.

This PR

1. Adjusts the demonstration application in demo/app/traini-cloud-microphysics.F90 and related files to process the ICAR training-data files that resulted from merging image-specific files into one regional file per 50 time steps;
2. Updates demo/train.sh to improve robustness by
   • Adding a check for the executable file and exiting if it's not found,
   • Adding default values for command-line arguments,
   • Removing unused command-line arguments, and
   • Updating to Julienne 3.6.1 to fix a crash that occurs when the network file already exists;
3. Adds file types to .gitignore;
4. Renames an example's supporting module to leverage default preprocessing;
5. Makes training output more verbose, including
   • more descriptions of intermediate steps and
   • printing epoch and cost function values.
6. Aggregates tensors across files for training.