Changed MemoryManager::alloc<T> to return Heap::T* instead of T*

Change-Id: Iede1ba624d1313fbe2f8e5e979e936f1f32efdc9
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Remove the remaining uses of Returned<T>

Change-Id: I493b75365d3c6fbf6965986d73e7aa0b659ded67
Reviewed-by: Lars Knoll <lars.knoll@digia.com>