This was causing hardly debuggable errors because names are transformed
to underscored lowercase names in the dbscheme and back to camelcase
for trap emission classes, which is not a noop in case uppercase
acronyms (like SIL or ABI) are in the name.
This makes the error be surfaced early with a helpful message.
The information that was contained in `schema.yml` is now in
`swift/schema.py`, which allows a more integrated IDE experience
for writing and navigating it.
Another minor change is that `schema.Class` now has a `str` `group`
field instead of a `pathlib.Path` `dir` one.
