ENH: support multi-zone motion (#2484)

- select motion for the entire mesh, or restrict to a subset
  of points based on a specified cellSet or cellZone(s).

  Can now combine cellSet and cellZone specifications
  (uses an 'or' combination).

- move consistent use of keyType and wordRe to allow regex selection,
  possibly using zone groups

STYLE: remove duplicate code in solidBodyMotionSolver