Overriding build_context() in preparation for subclassing FEMContext.
make check passing.
Adding AssemblyContext subclass of FEMContext. Not being used
yet.
Have build_context create AssemblyContext instead of FEMContext.
Cast to AssemblyContext instead of FEMContext.
init_context now takes an AssemblyContext in the Physics classes.
untabify
element_time_derivative takes AssemblyContext now.
side_time_derivative uses AssemblyContext now.
element_constraint now takes an AssemblyContext
side_constraint now takes an AssemblyContext
mass_residual now takes an AssemblyContext.
Most cache methods taking AssemblyContext now.
Moved boundary condition and vis stuff to AssemblyContext.
Last lingering conversions to AssemblyContext.
Merge pull request #57 from pbauman/assembly_context

AssemblyContext
Starting to think about refactoring CachedValues.