Instead of setting up the default keys by building the key struct

directly with a helper function in the cmd_entry, include a table of
bind-key commands and pass them through the command parser and a
temporary cmd_q.

As well as being smaller, this will allow default bindings to be command
sequences which will probably be needed soon.

cmd-if-shell.c

@@ -40,7 +40,6 @@ const struct cmd_entry cmd_if_shell_entry = {
 	"bt:", 2, 3,
 	"[-b] " CMD_TARGET_PANE_USAGE " shell-command command [command]",
 	0,
-	NULL,
 	cmd_if_shell_exec
 };