Resolves bug-report http://www.openfoam.org/mantisbt/view.php?id=1773

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

This reverts commit c5bea524.

This reverts commit b18f6cc1.

- mapFields and splitMeshRegions need more clarification

- operator[] with label -> get args at index
- operator[] with word  -> get named option

- ensure that the standard options (eg, from timeSelector) also have
  some usage information

- new optionLookupOrDefault and additional form of optionReadIfPresent
  with a default value

- markup codingStyleGuide.org examples so they actually indent correctly

- use 'Info<<' as per codingStyleGuide instead of 'Info <<'

- expose point field throughout

- make output less verbose, but can switch on/off with verbose() static method

- Unless the points(), cells(), patches() methods are called, the classes
  should know maintain a lightweight representation for as long as possible.

- bugfix: old-code used xferMove() instead of xferCopy() when creating the
  topology mesh - causing const pointField& to break if the code order was
  changed

- relocate blockMesh from src/meshing -> src/mesh

- also drop various unused time options from src/OpenFOAM/include

- removed the previously added fileName type(), isDir(), isFile() methods.

- added optional bool parameter to isFile() function to explicitly
  enable/disable the check for gzip files.

- fixed minor bugginess where the default usage of isFile() would result in
  false positive matches.

- be slightly more stringent and use isDir() and isFile() instead of
  exists() function when we actually know the expected type.

- can use 'XX.empty()' instead of 'XX.size() == 0', 'XX.size() < 1' or
  'XX.size() <= 0' or for simpler coding.
  It also has the same number of characters as '!XX.size()' and /might/ be
  more readable

- many size checking had 'XX.size() > 0', 'XX.size() != 0', or 'XX.size() >= 1'
  when a simple 'XX.size()' suffices

 - convertToMeters optional, also allow 'scale'