Turn extended keys on for tmux

So pi will stop complaining about it and so shift + return will just
work

config/tmux/tmux.conf

@@ -70,6 +70,9 @@ set -g set-clipboard on
 set -g allow-passthrough on
 setw -g aggressive-resize on
 set -g detach-on-destroy off
+set -g extended-keys on
+set -g extended-keys-format csi-u
+set -sg escape-time 10
 
 # Status bar
 set -g status-position top