Minor clean-up

- although this has been supported for many years, the tutorials
  continued to use "convertToMeters" entry, which is specific to blockMesh.
  The "scale" is more consistent with other dictionaries.

ENH:
- ignore "scale 0;" (treat as no scaling) for blockMeshDict,
  consistent with use elsewhere.

For multi-region cases the default location of blockMeshDict is now system/<region name>

If the blockMeshDict is not found in system then the constant directory
is also checked providing backward-compatibility

Upgraded other files as necessary for consistency with the blockMeshDict, in
particular cases with cyclic patches.