Graceful handling of saturated values in MODIS data

[mraspaud]

Is your feature request related to a problem? Please describe.
MODIS level 1B data has quite a few channels prone to saturation, leading to composites with gaps of invalid data.

Describe the solution you'd like
As discussed in #492, a solution would be to implement a modifier that would allow to perform the gap filling on the channels that need it.

Describe any changes to existing user workflow
One raised concern is how to let the users easily generate filled single-channels composites. Another thing to add is a DQF dataset to the hdfeos_reader so that the modifier would know which pixels to fill.

Additional python or other dependencies
Not as far as I can see atm.

[mraspaud]

This has been implemented since then.