Hide buttons when permissions are missing

I've noticed a couple places where the user sees the UI to do something, but gets a message that permissions are lacking after attempting to initiate the action. It would be better if the UI was not visible in the first place, especially if it's a multi-step action.

• Mute User button should only be visible to mods/admins/whoever can actually use it.
• Various actions in the clan that require clan permissions. For example, adding members to a group requires permissions, but the relevant tick boxes are still clickable in the UI. They should either be greyed out or displayed as text.