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.

.gitignore

@@ -0,0 +1,3 @@
+includes/config.inc.php
+database/config.sql
+site/.htaccess