Major reworking of vtkMultiBlockPLOT3DReader.

Added lots of new functionality including:
- Support for OVERFLOW files,
- Support for double precision,
- Auto-detection of the format of binary files.

Also cleaned up the code significantly.

Change-Id: I13a18c1afce8e3587529a385599084943f3f4143
Merge topic 'plot3d-reader-improvements' into master

50e677ac Major reworking of vtkMultiBlockPLOT3DReader.