Minor refactoring and features

• in SPHMultiset_CFD.hpp check the open boundary patch types
• add open boundary timers
• function computeTimeStep(args..) should be include in updateTimeStep()
• remove comments with capital letters in interactions and measuretools
• SimpleCellIndex takes 2D index_sequence as default, this should be part of specialized classes
• add sorted option to ParticleSet to check if object is sorted by other functions
• allow to write only selected fields
• use the correction matrix for MDBC in WCSPH_DBC
• in writeProlog initial time step shows zero instead the real value
• All model should be derived from particular template tailored to solver for which we implement the model.
• No-penetration BC has to be default part of WCSPH-BI model
• VTKWriter - write array should not require number of particles. The number should be taken from writeParticles function.
• Distributed particles in particle count rebalance mode should rebalance only based on percentage, not absolute value.
• Functions getStep and getTimeStep are confusing, rename them.
• WCSPH-BI should log all settings related to BC.
• The solver should report memory usage.
• Add None option to viscous terms