ENH: QDV for AMR -- Load Metadata
This commit introduces the first set of changes for Query-Driven Visualization (QDV) of AMR datasets. The changes are as follows: (1) The base reader implements RequestInformation() and defines a pure abstract method FillMetaData() to be implemented by concrete classes. (2) Concrete AMR readers implement FillMetaData() which essentially creates a vtkHierarchicalBoxDataSet with the uniform grids and AMR boxes but with no data, e.g., density etc. (3) The metada is published in the output information object for downstream modules.