Move configuration to a class so we can hang commands off it.

Signed-off-by: Chris Lamb <chris@thread.com>
Store all variants we create in a global variable.

Signed-off-by: Chris Lamb <chris@thread.com>
Add support for generating fallback nginx configuration.

Signed-off-by: Chris Lamb <chris@thread.com>
Add a utility for local installations to use the fallback mechanism too.

Signed-off-by: Chris Lamb <chris@thread.com>