Refactor waLBerla bridge

[jngrad]

Fixes #4859, fixes #4855

Description of changes:

• bugfix:
  • LB boundaries are now properly communicated in the ghost layer
  • see details in #4859
• performance:
  • the LB flag field is no longer communicated at every time step
  • the LB UBB field is no longer recalculated at every time step
  • LB boundary setters (node, slice, shape) now always trigger a full ghost communication
• maintainability:
  • the waLBerla header files are no longer visible in the ESPResSo core and script interface
  • the Boost dependency is now checked at the CMake level to prevent building broken ESPResSo shared libraries (see details in #4856)