libhb: Update nlmeans parameter string in test.c.
libhb: Add nlmeans strength and content tuning presets to test.c.

The four strength presets are ultralight, light, medium, and strong.
- Ultralight does its best to remove a small amount of noise without substantially affecting the look of the original picture.
- The others are fairly self explanatory.

The five tunes are film, grain, highmotion, animation, and none (or omitted).
- Film is suitable for all normal / live action content and removes slightly more chroma noise than luma noise.
- Grain passes the luma completely untouched and is nearly identical to film concerning chroma, only slightly weaker on account of leaving the luma noise. The appearance of grain is well preserved when used in conjunction with x264's grain tune. For a very slight grain reduction, try film on ultralight.
- Highmotion employs spatial-only filtering for the chroma channels in order to avoid color smearing between frames with very high motion (something which only becomes an issue at very strong settings) and is otherwise identical to film.
- Animation is good for cel animation and tries harder to remove artifacts around edges while preserving their overall fidelity.
- None uses equal strength for luma and chroma, and does not make any special adjustments for different types of content.

Presets are specified e.g., --nlmeans="medium" --nlmeans-tune="film". Custom (numeric) settings may be passed to --nlmeans, in which case --nlmeans-tune is ignored. Failure to specify any setting to --nlmeans uses the original filter default, 8:1:7:3:2:0.