Load branding preferences from API endpoint

The instance API response now includes the "config" dictionary as well as the the custom logo url. I have added code to set these values on the environment and raise a notification that the environment changes. The various UI widgets respond to the notification and change their colors accordingly.

I removed navBarTintColor from the environment and replaced it with primaryColor (and secondary color) to avoid confusion. The color may be used for more than just nav bar tinting.