Implemented Array:containsOnlyValue.
Restored implementation of ArrayOperations::memoryCompare on host.

Build of tools can be turned-off. Grid traversers for 1D and 2D has been rewritten using subdomain overlaps.

Implemented a method Array::checkValue which returns true only if there is an element with given value in the array.

Add StaticVectorFor - for cycle doing all combinations of directions

Heavy Refactorization of DistributedGrids:
	-> Reordered Directions
	-> Add some useless Direction helper functions
	-> Set Up DistributedGrid_Base - shared base with dim template parameter
	-> Add support for communicationGroup created for DistributedGrid (MPI communicator support)

Preapare Distributed Grids for Communication groups (aka MPI Communicator)

Fix Auto distribution when no distribution is specified.

Added parallel reduction to communicators.

Added command line arguments for a grid domain decomposition setup.

TNL compiles with MPI by default.

TNL compiles with MPI by default.

TNL compiles with MPI by default.

Conflicts:
	src/TNL/Problems/HeatEquationProblem_impl.h
	src/TNL/Solvers/PDE/ExplicitUpdater.h

It should not be called "base" because inheritance does not work for the
constexpr methods.