Consolidate multiple retrievals

The consolidate_class enables the consolidation of multiple satellite_class or insitu_class objects. This is used under the hood in the mulitsat_class and multiins_class but can also be used manually as follows:

>>> # imports
>>> from wavy.consolidate import consolidate_class as cs
>>> from wavy.satmod import satellite_class as sc
>>> # get satellite data rom s3a and s3b
>>> sco1 = sc( sdate="2020-11-1 12",region="NordicSeas",mission='s3a' )
>>> sco2 = sc( sdate="2020-11-1 13",region="NordicSeas",mission='s3b' )
>>> # consolidate obs
>>> cso = cs([sco1,sco2])

The same can be done with insitu_class objects.