Generify acolite by putting it in gips/atmosphere

[ra-tolson]

Fixes #393.

Also retain landsat's use of that code; this is in prep to make acolite work for sentinel-2. Other changes:

• Changed landsat's _products dict so acolite products can use either DN or C1, and made landsat always choose C1 over DN explicitly (used to do it implicitly, maybe, due to set()'s iteration order).
• Changed the asset used for the acolite system test
• Put timestamps in the sys test logging so we can see how long things are taking
• Deprecated VerboseOut in gips.atmosphere

[ra-tolson]

thanks much for the super-quick merge; cuts down on the rebasing pain later on : ]