Putting database in the GPU side

For the data store in the GridDatabase2D which is pointed by a SpatialDatabaseItemPtr *, _basePtr, in order to put the data in the GPU side, I made _basePtr a SpatialDatabaseItemPtr **. First, _basePtr will be modified by cudaMalloc, pointing to a memory address in GPU side, then, by launching a kernel, I will use new in the CUDA side to assign a chunk of memory in GPU to the pointer pointed by _basePtr. And the _cells member in GridDatabase2D is treated in this way as well.

The reason I do things in this way is because in the kernel, only addresses in GPU side can be accessed, therefore another indirect pointer is required.

For the reason above, all agents and obstacles have to be allocated in this way. So most of the interfaces in the original program will be modified.

Currently, I successfully assign the memory blocks for _basePtr, _cells, and obstacles. But for agents, I always encounter a kernel error when I was trying to launch them. I will keep looking into it. Hopefully, it can be resolved soon then I can run the whole program.