Added timer for GPU synchronization.

Added CWYGMRES solver (GMRES using Hauseholder orthogonalization and the compact CWY representation)

This reverts commit 40379dcf.

This will indicate to the user that the data will not be modified in the
solver. I think that it's not necessary to differentiate between e.g.
MatrixPointer and MatrixConstPointer, because these are implicitly
mutually assignable.

- base class with non-virtual destructor causes undefined behaviour
- missing return statements at the end of non-void functions
- missing const before char* function argument
- reordered initialization of class members
- misleading indentation after for statement
- fixed use of uninitialized variables
- fixed unsequenced modification and access to variables (the C++
  standard does not define the evaluation order of operands, so
  expressions with side-effects such as j++ cause undefined behaviour)

Plus the associated revamping of the SolverStarter. Also
ODESolverMonitor has been removed as its functionality has been merged
into the IterativeSolverMonitor.

Apart from squashing begin, end, entityOrientation and entityBasis
parameters into TraverserKernelData, this does not improve performance
of the LinearSystemAssembler, ExplicitUpdater etc., but in tnl-mhfem it
allows us to pass MeshDependentData, which is already available as a
SharedPointer, directly to the grid traverser without duplicating the
transfer to GPU.