Feature: Reactotron Settings screen

[jamonholmgren]

Currently, Reactotron has a Settings menu item that opens a JSON file (on my machine, it opened in Xcode, which was very slow).

This isn't a great experience. Make a Settings screen that exposes these options.

Possibly related issues: #1352, #1353

Stretch goal: go through Reactotron and Reactotron Core Server and stuff and make sure port 9090 isn't hard-coded (I think it is, because I think I did...lol)

[jamonholmgren]

Coordinate with #1353 to see if these should be separate screens (probably?) or combined into one. Add a way to easily access each screen if separate.