Speed up QV4::InternalClass

Speed up QV4::InternalClass

the old code used QHash to store the id to index
mapping, which got detached whenever a new internal
class gets created.

Replace this with a much cheaper custom made hash table.
The new hash table actually doesn't require a detach for
the first transition to a new internal class. This saves
significant memory and time esp. for very large objects
such as the Qt object.

Change-Id: Id1e3af4db59cff39d44ff1c211d46f37ff117ea6
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>