Refactor Mondo => Monzo

[JoeEcob]

Mondo was so 2 years ago, and it looks like the developer API is sticking around for a little longer so I figured it'd be nice to update the branding 😄

Mostly done by a bulk find / replace, with the odd authorization url changed here and there. Couple things:

1. The git repo and AppVeyor will need changing
2. The README links are currently pointing to a non-existent Nuget package - this will need creating
3. The version number will need changing - wondering if this should be major since it's a breaking change (thoughts?)

Any other ideas / complaints / suggestions let me know!

[JoeEcob]

Hey @rdingwall, is there any update on this?