TOS: allow users past error-case of tos.json

[davidangb]

The UI loads the TOS verbiage from GCS, in a file named tos.json. If - due to a blip in GCS or other weird networking issues - the UI can't load tos.json, the user is shown an infinite spinner and no way to proceed past the TOS gate.

Instead, we should show the "Accept" button even if the TOS contents haven't loaded, and offer a link to the TOS contents as hosted on the forums website.