Change js/appConfig.example so you don't have to remove `let`

[owenleonard]

JS variables defined using let cannot be redefined, but variables defined using var can. These changes allow the user to simply copy the file to their data directory and then change the settings they want to change. The settings in the data directory will override the default ones in appConfig.example.js.

I also moved the order the config files are loaded by index.html so the data file is given preference.