Should throw error when unknown permission is requested

[danfinlay]

Like a method not found error, maybe? Or do we want to support partial-resolutions? Might be nice to fail-hard by default, but allow a dapp to provide a parameter specifying that it's okay if a feature isn't supported, just leave it out?

Currently we display any unknown permissions to the user, and that's bad, b/c they could approve something that eventually becomes a permission.

[rekmarks]

I'm not sure if the "unknown permissions" are plugin-specific or dapp-specific. Please see the following PR: #87