Implement the splash page that is shown to first time users.
Frontend was done in https://github.com/mozilla/affiliates/commit/2716f20382179fa1e09048a6b147a5fa4f86083a, but the banner image still needs to be localized. Craig has made some progress on this and his work needs to be merged in.
https://github.com/mozilla/affiliates/commit/951ebfbe9f11f447a27da80e26a689d47a5b0b62 finishes this off with localized firstrun images. Note that the launch locale list hasn't been finalized, and doesn't match up with the images we have yet. In the meantime, this can be verified using the pt-BR locale.
Verified on pt-BR, de, pl, en, nl