If the Normandy Readonly server is being used, don't show edit buttons

[mythmon]

If the readonly Normandy server is being used (#297 and #298) UI that allows mutation shouldn't be shown, such as the edit button on the recipe page, and the approve button on approval requests.

We'll likely want to tie this into a larger permissions system in the future, but I don't think we are ready to do that right now until mozilla/normandy#1422 is ready. It may be good to keep this in mind while implementing the feature.