GENIE Gridspec Diagrams Mosaic

A mosaic consists of one or more "mosaicgrids". A mosaicgrid can either be a child mosaic, or a grid tile. Using this hierarchical mosaic concept, it is possible to represent a tree of grids for an entire framework, with each grid eventually ending with tiles as the "leaves". An optional grid descriptor may be used to apply a description to all tiles within a mosaic grid, e.g. "regular_lat_lon", "cubed_sphere".