Streamline User Input

[rmjacobson]

If we want to have multi-user/email support and multi-date range support, we're going to need a better way of inputting that information than the CLI. Right now, it seems like a config/input file is probably the way to go, but formatting might be a mess. JSON is always a good choice, and is already used in this project, but open to other solutions.

[rmjacobson]

Another thing to add onto this is how to deal with "optional" fields like the number of sites you need per campground. This defaults to 1, but if you need 2 or 3 or 10 what do you do? The input validation/sanitization needs to be able to handle this.