Added FilePad demonstration files in demos subfolder

demos/7_filepad/.gitignore

demos/7_filepad/A_cluster.yaml

demos/7_filepad/A_substrate.yaml

demos/7_filepad/B_cluster.yaml

demos/7_filepad/B_substrate.yaml

demos/7_filepad/C_cluster.yaml

demos/7_filepad/D_deposit.yaml

demos/7_filepad/PythonGoldCluster.ipynb

demos/7_filepad/README.md

demos/7_filepad/doc/FilePad_slides.pdf

demos/7_filepad/doc/PythonGoldCluster.html

demos/7_filepad/doc/gold_droplet_impact.mp4

demos/7_filepad/fig/010_deposit_gold_cluster_zoom.png

...ad/fig/020_deposit_gold_cluster_parametric_study_zoom.png

demos/7_filepad/infiles/A_minimize_cluster.in

demos/7_filepad/infiles/A_minimize_substrate.in

demos/7_filepad/infiles/B_equilibrate_cluster.in

demos/7_filepad/infiles/B_equilibrate_substrate.in

demos/7_filepad/infiles/C_melt_cluster.in

demos/7_filepad/infiles/D_deposit.in