Branding configuration

[adborden]

As a County Committee member, I want to be able to do some light customization of the app through configuration so that I don't need to fork the app and change code in order to launch my own Census Events app.

Configuration can be through the admin interface or through environment variable.

Acceptance criteria

• A logo can be provided by file upload and file specs are documented (e.g. use 200px x 200px png or jpeg)
• Site title can be provided which will be displayed in the header and within page titles
• Other attributes are relatively easy to add in the future
• Customization is documented in the site setup instructions