cleanup in boundary conditions

- introducing slab() function in concurr_common - common code to define subdomain ranges
- moving bcond.hpp to detail/bcond_common.hpp (and renaming the class)
- moving cyclic_common.hpp and polar_common.hpp to detail (+namespace)
- removing open_common.file - was not use anywhere
- moving shared bc to a separate file
- removing Doxygen headers from bc files