Str-elevs client

[ChanoOT]

A client class to read DEM pyramids is added (PyramidElevationDataProvider).
Changes in ElevationData and ShortBufferElevationData are done to save extra data from a DEM pyramid input file.
A new requestElevationData() method is added to make petitions based on tile information. Default behaviour redirects to the original method, the new class uses this implementation.
Minor changes in PlanetTileTesselator are done to make tile mesh resolution variable, according to the incoming elevationData. Default resolution is still the one given by TilesRenderParameters.
Minor changes in TileElevationDataRequest are introduced to call the new requestElevationData() method.
Minor changes in Tile are introduced to cancel elevation requests which are no longer needed.
Demo examples are introduced for every platform.

[ChanoOT]

@DiegoGomezDeck New changes done:

• Refactor of elevationDataRequest() methods into one which uses Tile pointer.
• Refactor of JSON-like DEM formatting parser so it is now placed in an external "JSONDemParser" class, as happens with BilParser.
• Correction of new code in tile.prune(), ensuring no memory errors will be produced.
• Removal of code warnings. Introducing some user-defined warnings in places to be improved in the future.
• Improving style-related issues and renaming of some elevationData extra fields.