Add user info dialog

This dialog would show useful things like:

• jabber id
• a way to change password (done: !330 (merged))
• status and status message
• Interface for changing avatar (#120 (closed))
• Server info: Which features/XEPs are missing?
• OMEMO fingerprints (#254 (closed))

This dialog could be shown for the user account, or with any contact we would like to get infos from.