Rename lilac modules to use `ctsm_` prefix

As per #869 we're going to rename all CTSM modules to begin with a `ctsm_` prefix. At first I thought we could skip this for LILAC, but now I'm thinking we should do this for LILAC modules, too. This is partly because LILAC is now a part of CTSM as opposed to its own repository, but more importantly because this seems more intuitive from an atmosphere model perspective: the main thing they are interested in is CTSM, so it makes sense for their use statements to begin with `use ctsm_...` rather than `use lilac_...`