[WIP] Multigrid support

[landinjm]

Do not review. Posted to collaborate with @fractalsbyx.

Summary of issues that are closed:
#394, #398. #386, #376, #409, #393, #294, #329, #313, #276, #290, #311, #301, #90, #273

Issues in progress
#351
#346
#323
#291
#285
#253
#218
#210
#174
#86
#65

[landinjm]

• Update CMakeLists.txt for new dependencies.
• Check perform of map, unordered map, and vector
• Add assignment and copy operators where useful.
• Add neumann boundary conditions
• Nonlinear solves

Checklist of features left to integrate

• AMR
• Newton update & nonlinear solves
• Multiple equations
• User-facing implementations
• Initial conditions
• Boundary conditions
• Grain growth features
• User-controlled inputs
• File read-in
• Checkpoints
• Transient problems
• Nucleation

[landinjm]

For the new variableAttributes we should test the most efficient method of lookup (see here) since the evaluation flags are passed for every cell.

[landinjm]

Should add more units tests for variableAttributes now that there's more working parts

[landinjm]

Should also break up type_enum.h

[landinjm]

Merging into devel to continue work there