Added a new reader to better handle PLOT3D files.

- Added a new reader (vtkPlot3DMetaReader) designed to make it easier
to deal with Plot3D files. This is a meta-file in which the user
can specify various settings (such as endianness, multi-grid etc.)
rather than having to do it through the reader API. The reader also
supports time series of xyz and q files.
- Added JSON CPP support which is used by the meta-reader.

Change-Id: I991e6487869966c3e1769835a72fd2f8b7f81770
Merge topic 'plot3d-meta-reader' into master

452d8812 Added a new reader to better handle PLOT3D files.