Move argparse code into separate `argparse` modules

Functions and classes handling command-line argument parsing using the `argparse` module as the base are peppered throughout the database. Functions named like `argparse_*`, and classes like `*ArgumentParser` and `*Action` reside either in `__init__.py` or `misc.py` files. If we move them to separate `argparse.py` files in each corresponding package, we could make each affected file shorter and more [cohesive](https://en.wikipedia.org/wiki/Cohesion_(computer_science)).

This is done when all listed and related functions and classes are moved to `argparse` modules in each of their packages, and all references of them are updated.