Allow host memory to be used for property data

[rlratzel]

Who: end users
What: use host memory on both a single node and a multi-node cluster in order to store property data that shouldn't occupy GPU memory
Why: Properties are not needed in GPU memory for cugraph algo calls, and will greatly reduce the max graph size if stored in GPU memory. If a user can instead store property data in host memory, this frees up GPU memory needed for graph structure data, allowing for much bigger graphs.

User story: "As a user, I need to use host memory on both a single node and a multi-node cluster in order to store property data that shouldn't occupy GPU memory."

### Tasks
- [ ] rapidsai/cugraph-pg#9

[rlratzel]

The original story points assigned to this was 21, so a new research story #14 was created. This story depends on #14.