[KB] mapping of CTS URNs

The KB contains several legacy custom URNs that need to be mapped to Perseus Catalog's CTS URNs. The full list can be found [here](https://github.com/mromanello/hucitlib/blob/master/hucitlib/data/misc/urns_tofix.txt). For example, `urn:cts:cwkb:535` needs to be mapped to `urn:cts:latinLit:phi0926`.