Split some of getSettings into makeRequest
Split some of getSettings into makeRequest

In preparation for add a function to modify settings that will also need to
make requests. I've moved authEmail, authKey and zoneID to global variables
so that we don't have to pass them through several functions. Unsure about
this, but it seems like the best solution.

alphagov/cloudflare-configure,alphagov/cloudflare-configure