This is the first MR in a series to implement #26 (closed).
The solver interfaces use dynamic polymorphism, but currently it is not possible to fully benefit from this feature. We want to allow the user to take full benefit from a dynamic interface for solver/precoditioner/scalarproduct/linearoperator.
The main change is that the category isn't an enum anymore, but virtual method catergory().
This MR contains the following changes:
new method category() to check for the same SolverCategory of different components at run time. This is a slight drawback compared to the current compile time checks, but it adds a lot of flexibility as we will be able to write factory classes for solvers and compose/exchange solvers at runtime.
add SolverCategory::category(object) to be be backwards compatible
add a cmake switch to enable/disable the backwards compatibility
update solvers to the new interface
update preconditioners to the new interface
update scalar products to the new interface
update operators to the new interface
update AMG implementation to the new interface
remove static dependency of PropertiesGraphCreator on the category
