Complete mklib toolchain in LibraryBuilder.

First, LibraryBuilder now makes lib.dat for mklib.

LibraryBuilder manages two directories now: the `input_dir` where
each StarFISH run is performed, and an isochrone prep dir holding
the raw isochrones.

LibraryBuilder also cleans the output isochrone dir `iso/` of
pre-exisiting isochrones before installing the new set.