Show media quota info in Settings

MSC4034 defines new interfaces for querying the user's media quota information on the server. Now that MMR supports this, we should add it to Circles.

Not all users will be logged in to servers that support the new API features. But if the servers supports it, we should expose this information to the user. On the Settings screen, we should add a new section called "Storage". Under there, we should show the user's maximum and current usage.