Adds Cassini Vims driver for use within ISIS (#466)

* Added cassini vims vis/ir drivers

* Various cassini vims centric driver changes

* fixed rebase conflict

* Finalized cassini vims drivers

* Added cassini vims test data

* Added tests for cassini vims

* Updated cassini vims tests after pck loading order change

* Changed env var monkey patch from ISIS3DATA to ISISDATA

* Fixed typos in doc strings

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Co-authored-by: acpaquette <acp263@nau.edu>
Co-authored-by: acpaquette <acpaquette@usgs.gov>