Unittest - Enhanced support for testing hooks (wip)

* It is now possible to test:
  * Hook Input/Output on STDIN/STDOUT channels
  * Exit code of hook script
  * Execution count (how many times the hook was executed)
  * Timestamp execution (when was the hook executed - milisec resolution)

test/test_hooks/on-exit.dummy

@@ -0,0 +1,9 @@
+#!/bin/sh
+
+echo "on-exit executed"
+
+while read TASK; do
+    echo "New/modified task $TASK"
+done
+
+exit 0