Add NH GRANIT othorimagery and lidar hillshade layers

[zekefarwell]

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This adds orthoimagery and lidar hillshade imagery layers for the US state of New Hamshire available from NH GRANIT, New Hampshire's statewide GIS clearinghouse. I've confirmed with NH GRANIT that these datasets are available in the public domain and have no restrictions on their use (documented on the OSM wiki here). I've added these same layers to the JOSM imagery sources as well.