Change install path from prefix

[Kelvinrr]

Ran into some issues trying to use the plugin with ISIS where the default install location is in lib where ISIS wants it in lib/csmlibs/3.0.3/

would it make sense to update CMakeLists.txt to install into $PREFIX/csmlibs/<csm_version> ?

[jessemapel]

I think this makes sense. This may or may not resolved conda-forge/usgscsm-feedstock#10