Add MCLS to Denovo Stratimikos solvers.

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MCLS has implemented the Trilinos Thyra interfaces. Denovo leverages Stratimikos for parameter list driven generation of linear solvers that implement these interfaces at runtime. MCLS needs to be added to the Denovo build and solver classes for use with the SPn equations.

Definition of done: build Denovo with MCLS as an optional dependency and run an SPn problem using an MCLS solver.

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Working on this now.

MCLS is either checked out in the top-level Exnihilo directory or soft-linked to its actual location. A configure time flag enables the code added to StratimikosSolver.cc

MCLS is listed as an optional dependent library for the kba solvers subpackage

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The code is building with the additions. A unit test is next to check functionality.

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The tests are written and passing in parallel. Tom will review the branch and merge with the master if ready.