[PL] added new BC classes

ProcessLib/BoundaryCondition/BoundaryCondition.cpp

ProcessLib/BoundaryCondition/BoundaryCondition.h

ProcessLib/BoundaryCondition/BoundaryConditionCollection.cpp

ProcessLib/BoundaryCondition/BoundaryConditionCollection.h

ProcessLib/BoundaryCondition/BoundaryConditionConfig.h

ProcessLib/BoundaryCondition/CMakeLists.txt

ProcessLib/BoundaryCondition/DirichletBoundaryCondition.h

.../BoundaryCondition/GenericNaturalBoundaryCondition-impl.h

...ssLib/BoundaryCondition/GenericNaturalBoundaryCondition.h

...Condition/GenericNaturalBoundaryConditionLocalAssembler.h

...b/BoundaryCondition/UniformDirichletBoundaryCondition.cpp

...Lib/BoundaryCondition/UniformDirichletBoundaryCondition.h

...Lib/BoundaryCondition/UniformNeumannBoundaryCondition.cpp

...ssLib/BoundaryCondition/UniformNeumannBoundaryCondition.h

...Condition/UniformNeumannBoundaryConditionLocalAssembler.h