Initial import of tasks application

This initial import is a heavily modified version of the code I had
here, as Arse was modified for other purposes in the meantime and the
application no longer worked with it.

In addition:
 * I did not import the user management part yet,
 * task dependencies are supported in-base, but there is no interface
for that yet.

includes/t-users/package.inc.php

@@ -0,0 +1,5 @@
+<?php
+
+$package[ 'requires' ][] = 'core';
+$package[ 'files' ][] = 'users';
+$package[ 'daos' ][] = 'users';