Added some zero checks to Memory implementaion

Change-Id: Id6bab33611863a83df08f9b62bff2652b617820f
Add ConstIterator to Vector

Change-Id: I91b9a668228de18e64f1437d2d305b89e00e2c04
Add decrement operator to iterator of vector

Change-Id: Ifacfab070d8ed1e590326e02fe820368de117b43
Add erase methods to vector

Change-Id: Ibce088872db6fe91cfa563b279f4867c428d0fe7