Add GeneratingTileLayer

[jericks]

A TileLayer that can generate Tiles on demand as a client tries to get them. It would be wrap a TileLayer (like MBTiles) and a TileRenderer (like ImageTileRenderer) and if the client tries to get a tile that isn't present (doesn't have any data) it would use the TileRenderer to generate the data.

MBTiles mbtiles = new MBTiles(new File("world.mbtiles"),"The World","The World Tiles")

Workspace workspace = new geoscript.workspace.GeoPackage(new File("naturalearth.gpkg"))
Layer countries = workspace.get("countries")
countries.style = new SLDReader().read(new File("countries.sld"))
Layer ocean = workspace.get("ocean")
ocean.style = new SLDReader().read(new File("ocean.sld"))

ImageTileRenderer renderer = new ImageTileRenderer(mbtiles, [ocean, countries])

GeneratingTileLayer generatingTiles = new GeneratingTileLayer(mbtiles, renderer)
generatingTiles.get(0,0,0)
generatingTiles.get(1,0,0)
generatingTiles.get(1,0,1)
generatingTiles.get(1,1,0)
generatingTiles.get(1,1,1)