Enable the usage of double width or double height blades in server chassis

[phgrau]

With this patch, it is possible to define a double height blade in a server chassis, by specifing the used slots in the object definition (e.g. Slot: 8,16 for a HP Proliant BL 680 Blade in a c7000 chassis).

I applied the modifications to a vanilla racktables 0.21.5, and suddenly my server blades where displaying correctly. I assume the rest of the code for the old "slotpatch" change made it into the main code some time ago, but this peace was missing.

Regards,

Philipp