tmux: Use shell script to complete selfinsert

Use a short shell script to complete the `selfinsert` keytable by
binding all keys that have a mapping in the root table.

.config/tmux/tmux_selfinsert.sh

@@ -0,0 +1,8 @@
+#!/bin/sh
+#
+# Create a key-table which self-inserts all keys that are bound in the root key
+# table. (C-h for example is sometimes needed as backspace sequence)
+
+tmux list-keys -T root | awk '{print $4}' | while read key; do
+	tmux bind -r -T selfinsert "$key" send
+done