filter_obs, unit conversions and other transformations not applied to satellite obs.

[blychs]

Hi all,
In the current version of the code,

self.mask_and_scale()
self.rename_vars()
self.sum_variables()
self.resample_data()
self.filter_obs()

are only applied to open_obs() in the class observation

However, currently we have another function, open_sat_obs() for the satellite observations in the same class observation.

I think that there are two possible, simple solutions.

a. Add the same to open_sat_obs()
b. Doing those steps in the class analysis, when we call open_obs there.

Let me know what you think
Cheers
Pablo