Initial implementation of CylindricalAirgap class which automates creation of multiple annuli between two radii

Problems with discontinuous material boundaries have fields which suffer from jump discontinuities
This means the divergence of the Maxwell stress tensor is impulsive at material interfaces
Evaluating net force/torque using body forces requires both volumetric and surface integrals in these cases
This is a nontrivial excercise

In the meantime, the next step will be to add a special calculation method for cylindrical airgaps

Store FiniteElementMesh DiscreteRegions in std::map with Contour as key

Changes the way number of elements and unknowns are calculated in Physics
    This still needs some work
Adds FunctionArgument class for passing arguments to Forcing objects with multiple parameters
Adds test demonstrating parallelism using OpenMP

FiniteElementMesh remains templated to facilitate storage of variable order elements

    Part of this involves using more shared pointers and vectors (as opposed to arrays) as certain member variables
    Some of that has been done, some work may (probably) still needs to be done
    It's been a few months since this has been looked at so it will require some review

This is a bit of a mess right now

Work on rotational motion and related boundary refinement
Output for vector plots
Starts on nonlinear material properties
Begin encapsulating solver routines

Mesh::smooth() is based on satisfaction of a Laplacian condition

MappedBoundaryPair guarantees correct behavior of PeriodicBoundaryConditions when the UniformDiscretization option is set to false

Implement more rotational motion tests