Add support for kernel with multi-level indirection

[jyoung3131]

We would like to support sparse accesses that have a second level of indirection, such as with an array of pointers or a pointer to another pointer.

Based on further discussion we think that this could be implemented within a kernel with a nested loop.

Additional requirements include:

• Index arrays might be different sizes unlike with concurrent G/S
• May need to make some improvements to JSON input format to enable this
  • Binary file input or synthetic addition to JSON
  • Dependent on #80