File downloaders rework

[EvilDrPurple]

Context

Our file downloaders could use a bit of a rework. They seem overly complex and only able to support a few different file types; with various modules calling to each other and requiring a specific order that is unclear. Not to mention all the defunct scripts littered about. I believe a much more straightforward approach is possible and will go a long way in helping people understand how and when to use our util modules. During work on #227, I found this way that will download any file type when provided with a download url:

r = requests.get(url, stream=True)
with open(file_path, 'wb') as fd:
    for chunk in r.iter_content():
        fd.write(chunk)

SEE: downloaders.py, get_files.py, muckrock_scraper.py

Requirements

• Should be simple and easy for people to understand how to consume the module(s) and how they work
• Should be clear what modules, in what order, and when they should be called
• Should not break any existing functionality of scrapers or other util scripts

Docs

• Docs related to the file downloaders and util scripts should be updated where necessary
• New docs should be written to explain how to use and consume the file downloaders

Open questions

• This will likely be time consuming to understand what's going on with the code, what functionality should be kept, and how to untangle it
• Perhaps think about keeping an entire pipeline of functionality in one folder for organizational purposes