Added new features:

• Use argument parser and new arguments:
  • --cache directory will be tried before downloading from internet
  • --dst change destination directory
  • --list list all model names
  • --cleanup remove all tar.gz files afterwards
• Add hierarchy to model structure, now there are regular models which can be downloaded directly and archived models which should be downloaded and then required files will be extracted. Archived files will be checked for existence before downloading whole archive - it allows to populate them from cache and avoid storing archives on disk.
• Filters are now case-insensitive and use contains rule for matching, multiple filters can be used in the command line, results will be united.
• GDrive object simplified to separate method - allows to reduce repeated download code. Better solution would be to extract all download-store-verify functionality to separate class(es), but I decided to postpone this step for the future improvements.
• Use pathlib.Path for most paths.

I have doubts regarding filter arguments: should we keep them positional arguments or change to keyword arguments (e.g. --filter)?

Examples:

# Populate cache and remove archives afterwards (~4Gb)
./download_models.py --dst /data/dnn --cleanup
# Download models to the specified folder using cache
./download_models.py --cache /data/dnn --dst $HOME/opencv_extra/testdata/dnn
# List all models having face in their name
./download_models.py --list face

Note: also updated my p2p model distribution project - https://github.com/mshabunin/opencv_models_p2p