add: tool to validate if declared opposites exist

tools/validate_opposites.sh

@@ -0,0 +1,17 @@
+#!/bin/bash
+
+opposites=$(cat relationships/definition.json | grep '"opposite"' | cut -d ':' -f 2 | tr -d ' ' | tr -d '"')
+
+for opposite in $opposites
+do
+  cat relationships/definition.json | grep '"name": "'$opposite'"' >/dev/null 2>&1
+  res=$?
+  if [ "$res" -eq 1 ]
+  then
+    echo "'$opposite' not found"
+    exit 1
+  fi
+done
+
+echo "OK, all opposites seem to point to existing relationships"
+exit 0