client: improve server connection status messages

client: improve server connection status messages

Always logs various errors and rejections that previously were only
visible with developer cvar(s) set.  Among other things this fixes
silent failure when trying to join a full server.
Includes IP address in more messages.

Uses CON_ERROR and CON_WARN colours for various errors and warns.

Moves status message generation to the code that sets the relevant
states.  This allows more information to be included, makes the code
easier to follow and reduces polling.

Fixes some cases where a message was always clobbered before it could be
displayed.

Merges the built-in menu and loading screen connection status generation
and buffering.

Simplifies challenge request retry counting.

Signed-off-by: bones_was_here <bones_was_here@xonotic.au>