Move vtable out of internalClass

Move vtable out of internalClass

We can move the internalClass to Object later on, and such save
having the internalClass on lots of Heap objects.

This commit basically adds and starts making use of a new
vtable pointer in Heap::Base. In addition, the construction
methods in the memory manager now automatically setup the
correct vtable.

Removing the vtable code from InternalClass and moving it into
Object will come in a separate commit

Change-Id: If49e8d73c769bf65bf47fe4dbf8b9546c8019dbc
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>