Vastly improved the pokedex import/export UI.

csvimport is now load; csvexport is now dump.

Both take an optional -e switch to specify an engine, but will happily
use a default SQLite database in the pokedex package directory.

Additionally, the CSV directory is now controlled by the optional -d
switch, and defaults to Doing The Right Thing.

So `pokedex load` now does exactly what you'd expect: loads the data
from the right files into a consistently-located database.