Changed fastNlMeansDenoising and fastNlMeansDenoisingMulti back to sum of sq distances. Moved sq sum of abs distances to fastNlMeansDenoisingAbs and fastNlMeansDenoisingMultiAbs

Preparation for 16-bit colored denoising. Currently not working due to cvtColor not supportint 16-bit Lab conversion.

Basic 16-bit implmentation of fastNlMeansDenoising. Table-based exponetiation leads to high memory footprint and loss of precision in 16-bit mode.

use `bash` shell instead of `sh`, since on Ubuntu `sh` by default is `dash`,
and `dash` doesn't support `PIPESTATUS` feature used in this sctipt