add convenience forward/reverse dep listers

dot_local/bin/executable_xxdeps

@@ -0,0 +1,2 @@
+#!/bin/sh
+xbps-query -Rx "$1"

dot_local/bin/executable_xxrevdeps

@@ -0,0 +1,2 @@
+#!/bin/sh
+xbps-query -RX "$1"