Cross-browser support for Frame.io Login

While this won't be relevant for fully API-driven applications, Frame.io's cross-browser support does come into play when loading our Accounts app during an OAuth credential grant flow.

When writing OAuth applications for Frame.io, please be aware that the login page we present in the OAuth flow will adhere to the same browser support as our main web application. For the purposes of the below, "Partial" support means all major functionality should be unimpeded, but some minor layout issues may be present. "Minimal" support means it might work, but we no longer explicitly test or support it.