Adding tnl-view tool.

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

Adding directory legacy for old code.

Implementing PDE solvers and time steppers.

Changing explicit solvers - Merson and Euler.

Adding simple template of project with Makefile to examples.
Adding cmake tests for PETSc for testing of solvers.

Renaming tnlArray to tnlMultiArray.

Finishing new template interface for GMRES.

so far).