Indicate security updates in plain-text output

Add a fourth column to package.txt, indicating whether an update is a
security or a normal update.

Signed-off-by: Apollon Oikonomopoulos <apollon@skroutz.gr>
Inventory: add resources for Dell servers

Add Driver and Support links for all Dell servers. The interface is
generic enough to be extensible for other manufacturers/resource types.
The template renders all (<description>, <url>) tuples under
host.resources accordingly.