Created geotools transformer and injected it into the tile renderer

This pull request is on the basis of https://github.com/deegree/deegree3/pull/442 . The other pull request should be dealt with first as this one just adds the geotools transformer.

A geotools transformer (class: GeotoolsRasterTransformer; implements ImageTransformer) was implemented to transform raster images from one envelope to another envelope. As the name of the class already implicates, the transformer uses the geotools library (which is currently not present in the deegree nexus).

There are several reasons why geotools was chosen to do the transformation of a raster image:
 * Raster tranformation is a complex feature which is tackled by geotools quite good (why should I implement my own RasterTransformer?).
 * The API of raster transformation is simple in geotools.
 * There is a raster transformer in the coverage API of deegree, but its implementation has several drawbacks (complex API, not documented well) and did not work well with the tiling API (axis order was a big problem).
 * The quality of the result image is better with geotools than with the raster transformer of the coverage API.

Finally, the geotools transformer was injected into the Java2DTileRenderer (in class DefaultRenderContext) and is used to transform tile datasources.