Make the config dependency's origin

Set in global namespace from a script tag rendered by Rails app
Extracted bytesToSize from common to header

Since only used there
Added upgrade URL

- Created navigation model since there will be more navigation URLs, a
specific view should not need to know how to construct them (there’ll
be more).
- Extracted Header view from Main view since it is only instantiated
once, no motivation to couple them.
- Added/updated tests