Landsat

Closes #52 (closed)

Landsat processing now ready and working. Masking based on bit indices implemented in mask.py and explained in landsat.rst. Config file for landsat now works with collection 2 and at least level 2 data but should work with level 1 as well. Config file for S2 also changed regarding new "general" changes to the config (such as adding filepattern and flag for bitmask). Some changes in other files as well, for example generalization in userinput.py.