Make 'Anonymous Coward' configurable

Make the username that is displayed for users that haven't set a full
name configurable.

'Anonymous Coward' that was hard-coded in Gerrit before was seen by
some users as unprofessional and insulting. This is why for corporate
environments it makes sense to configure another name.

Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>
Change-Id: Ib2edee2af342b17df676e87cef99f92448895abe
29 files changed