add write support to the geotiff plugin

Add write support to the geotiff plugin. There is a complication to this deceptively simple-sounding proposition, and that is the encoding of CRS information from the Geotools representation to the GeoTIFF representation. Geotools has authority factories which create complete CRS objects from authority codes, but does not have a facility for examining an arbitrary CRS to determine if it "happens to match" an authority code. Since GeoTIFF's default mode is to store the CRS information as EPSG codes, the "best" way to implement a GeoTIFF writer is to use EPSG codes whenever possible.

There are fallback positions available, however: GeoTIFF also supports user defined CRS. (Note: the degree of "user defined" support offered by any given software package is not necessarily guaranteed.) A first cut at a GeoTIFF writer could accept only those grids created by an EPSG authority factory (these CRS objects retain the EPSG code). A second cut could include support for user defined coordinate systems. The final version would compare the CRS to the EPSG authority and retrieve a code if possible.

A number of subtasks have been identified, each of which requires it's own unique skillset. Absolutely required is a means to encode GeoKey information in the GeoTIFF's IIOMetadata object. Everything else follows from that. The subtasks are described further on their own pages.