Implementation of TimeIndependentPDESolver.

* parallel-reduction:
  Fixed ArrayOperations::compareMemory for MIC
  Fixed parallel reduction for MIC
  General parallel reduction on host
  Refactoring parallel reduction operations

- used variadic templates to avoid code bloat
- added execHost static method to avoid nvcc warnings

- separate data types for input arrays of binary operations
  (necessary for the equality comparison of two arrays of different
  type)
- added separate template parameter for ResultType, which defaults to
  the RealType
  (the goal is to allow sum of bool vectors into int instead of bool)

Long live clang for pointing this out!

Standard CMAKE_CXX_FLAGS are a space-delimited list, but our
CXX_TESTS_FLAGS are manually passed to CUDA_ADD_EXECUTABLE, which
expects a semicolon-delimited list. Blame cmake for such a crazy
language...