User should not be able to register the name "quiet"

[holmesworcester]

We are using the "Quiet" username for "new user joined" messages and potentially other messages in the future, like welcome messages. We should reserve this name so that a normal user cannot also register the name "quiet".

This can wait until we add custom user profile images, because until we do it will be very clear that the Quiet user is special and impossible to spoof it, since it has its own special profile thumbnail image that is distinct from generated images.

Requirements:

1. Attempting to register username Quiet returns "name taken" error.

2. If a registrar does register the username Quiet, clients should ignore those messages and display a warning that registrar may be malicious.

[kingalg]

@holmesworcester maybe this task would be a good one to do with out current tasks for unregistered and registered users as this is also connected to naming and security? It could reuse design that we have for duplicated names, just with different message. With this we would cover topic of "not malicious names" nicely.

[holmesworcester]

Let's wait until we have custom profile images, since it isn't really needed now.

[leblowl]

Just noting that this issue seems relevant now