[vali] finish the slab allocator and switch to it

[Meulengracht]

As memory management is becoming an increasingly bigger priority to get stable, fast and robust memory management, I have started working on a simpler and more sophisticated allocator, located in tools/slab/slab.c for now. Right now locking and list management is missing, but core functionality is almost done. After fixing the VMM systems in vali as we are currently doing, switch the new memory allocator in.