ENH: Adding reader plugin for (a large part of) the LLNL's GMV file format

     Reader is independent of VisItBridge, but it does rely on the same I/O
     library the original author of General Mesh Viewer released a few years
     back and includes it from the VisItBridge's GMV reader source directory.

     Features:
     * NODE and CELL based data is supported, no FACE based data. Simply
       because among the various GMV files generating codes the plugin was
       designed for there was none that produced FACE based data. An according
       warning is raised if a GMV file contains FACE based data.
     * File series supported
     * Builds for OSMesa builds as well (issue 13393)
     * Currently support for the following GMV keywords
          GMVINPUT [ASCII|BINARY]
          COMMENTS
          ENDCOMM
          NODES
          CELLS
            LINE
            TRI
            QUAD
            TET
            HEX
            PHEX8
            PRISM
            PYRAMID
            GENERAL
          NODEIDS      [not supported by VisItBridge's GMV reader]
            IDS(NNODES)
          CELLIDS      [not supported by VisItBridge's GMV reader]
            IDS(NCELLS)
          MATERIAL     [numeric values are imported, not material names;
 	               unlike currently by VisItBridge's GMV reader]
            [DATA]
          VELOCITY
            U(NCELLS)
            V(NCELLS)
            W(NCELLS)
            U(NNODES)
            V(NNODES)
            W(NNODES)
          VECTORS N components
 	              [not supported by VisItBridge's GMV reader]
            DATA1(NCELLS or NNODES)
            ...
            DATAN(NCELLS or NNODES)
          VARIABLE
            [DATA]
          ENDVARS
          FLAGS        [names are imported, not numeric values,
 	               unlike currently by VisItBridge's GMV reader]
            [DATA]
          ENDFLAG
          POLYGONS     [not supported by VisItBridge's GMV reader]
            MATERIAL_NO
            NVERTS
            X
            Y
            Z
          ENDPOLY
          TRACERS
            X
            Y
            Z
            DATA
          ENDTRACE
          TRACEIDS     [not supported by VisItBridge's GMV reader]
          PROBTIME     [not supported by VisItBridge's GMV reader]
          CYCLENO      [not supported by VisItBridge's GMV reader]
          CODENAME     [not supported by VisItBridge's GMV reader]
          CODEVER      [not supported by VisItBridge's GMV reader]
          SIMDATE      [not supported by VisItBridge's GMV reader]
          ENDGMV

       All other keywords are silently ignored, i.e. no warning is displayed.
       Cells can be given explicitly (unstructured mesh) or implicitly
       (structured regular brick meshes and logically rectangular brick
       meshes).
Simplify Plugin CMake contribution

Change-Id: Ic528417131647a1890c86a60b78446ff8ed65eb1
Move forward visitbridge to fix warnings

Change-Id: I52e02dba7c4d1edefcb18b2a738a1e1a8493c17b
Add GMV Reader testing

Change-Id: I326b954577fcbba0e5da95f35c7643a9feec6c7f
Merge topic 'integrate_gmv_reader_contribution' into next

89b1ad2 Add GMV Reader testing
b4d1e1a Move forward visitbridge to fix warnings
205602d Simplify Plugin CMake contribution
dcb4509 ENH: Adding reader plugin for (a large part of) the LLNL's GMV file format