Replace warning message "you can't change your friendly name" with something less obtrusive

[diederik]

When a friendly name can't be edited, a popup is displayed to notify the user about this. It has a "do not show this message again" checkbox, but it's still too obtrusive.

Instead we need to find a way to make this clear to the user while not blocking his workflow. (perhaps some inline note in the account settings panel)

[amroth]

Fixed. This patch completely avoids nickname changes if the account is not verified; therefore the problem should be gone.

[amroth]

Btw, the Account Settings already forbid changing the nickname manually. The patch just extends checking at a lower level - may avoid other problems, too.

[valerio]

Fixed with r2334.