[In Progress] Scraping, Reference Ranges and Units

This is a pull request in progress. This PR includes work for practice and provider scraping (fixes #87), reference ranges (fixes #53) and units(fixes #82). I was almost done with scraping, but I decided to put more effort to scrape all the information I can find online. 

For reference ranges and units, there is more work to do. I have designed what I will be doing for units. For reference ranges, I will work on the front end and connecting reference ranges to record update values.
I'd also prefer to make these arguments consistent—`update` and `section` are classes, but `field_name` is a string. I'd replace `field_name` with `field` (of class `RecordSectionField`). It's just more modular then.