Implement has_edge() & compute_multiplicity()

[seunghwak]

graph_view.has_edge() query whether the graph has given (src, dst) pairs as edges.

graph_view.compute_multiplicity() query the edge multiplicity of given (src, dst) pairs (assumes that multiplicity is 0 if there is no edge between a given pair). This function throws an exception if graph_view.is_multigraph() is false (better use has_edge() for non-multigraph).

In addition to adding the above two functions, this PR includes few code cleanups.

• major_idx_from_major_nocheck() to edge_partition_device_view_t
• Move count_invalid_vertex_pais from nbr_intersection.cuh to error_check_utils.cuh
• Update cugraph::test::to_host, to_device, device_gatherv, and device_allgatherv to support bool type (and to handle std::vector<bool> which stores bool values in a packed format)

[seunghwak]

@jnke2016 I need to write tests to merge this PR but you can use this PR to continue K-truss implementation.

[seunghwak]

@jnke2016 Now this PR is ready for your testing in K-truss.

[ChuckHastings]

/merge