This way they can use either yes/no, on/off, or true/false.

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

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

There is shor test of this stuff for 1D 2D and 3D.

Relpaced tabs with 4spaces.

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...