Various bilinear scale interpolation fixes

[aaime]

This pull request covers:

• https://github.com/geosolutions-it/jai-ext/issues/204
• https://github.com/geosolutions-it/jai-ext/issues/202
• https://github.com/geosolutions-it/jai-ext/issues/201
• https://github.com/geosolutions-it/jai-ext/issues/200

It also partially covers https://github.com/geosolutions-it/jai-ext/issues/203 but I believe there are likely still some outstanding logic changes needed.

[dromagnoli]

Replaced by #209