Clouds not correctly masked for Sentinel-3 images

[bert.coerver]

Pixels with an uncertainty larger than 2.5K in the LST values are currently masked, but the defined uncertainty for cloudy pixels is necessarily larger than for clear sky pixels. So clouds aren't being masked correctly.

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[bert.coerver]

Added extra step to mask clouds, https://bitbucket.org/cioapps/pywapor/commits/45b2439b455681abb82c5a5e4a2b5f9691ae0a15