Refactoring the Dirichlet and the Neumann boundary conditions.

Min. interations feature was fixed in the GMRES method.
Timers for explicit and semi-implicit timestepping were added.

Adding --fast-build optin for the build script to speed-up compilation.

Adding an exception to tnlAssert.

Explicit instantiation of template CUDA reduction.

Adding explicit template instantiation.
Moving some _impl.h files into implementation dir.

Adding directory legacy for old code.

Creating template GMRES solver.