Initial ADIOS readers and writers

This is a first pass at readers and writers using the ADIOS library.  It
currently supports writing vtkUnstructuredGrid, vtkImageData, and
vtkPolyData.  The same types are supported for reading into a
vtkMultiPiece dataset. Requires ADIOS version >= 1.7.0.

Currently known issues to be addressed in further branches:
- FindADIOS.cmake was taked directly from the ADIOS source and needs some work
- Setting the writer to WriteMode = OnChange produces output not compatible
  with the reader
- All pieces must currently have the same type of data
- Reader will read all arrays, no way to currently select which arrays to read
- Additional VTK datatypes to be supported

Change-Id: Ib5603d1708a59df923267990ebccc65299fbb6e4
Merge topic 'new_adios_readers_and_writers' into master

4eb181fc Initial ADIOS readers and writers