Configuration GUI

This is a super quick and dirty addition of a form to allow for updating the available settings and then regenerating the current image.

This exposes all of the available settings and the `sourceLoadComplete` function to the global, `window` scope. `sourceLoadComplete` is renamed to `regenerate` in the public API.

Exposing those items to the window scope allows for updating settings and regenerating via the dev console:
- Open up the console
- You can see what's available by logging `api`. Just type `api` and hit enter
- Change any of the setting values with api.SETTING_NAME = NEW_VAL
- Then run `api.regenerate()`

I didn't do much testing with this, just got it to a working point in the latest chrome. Styles for the form are fairly wonky.