squee, returns all data as strings, and expects strings as inputs to
queries. So, keeping the ids as strings was easy initially, but it means that
you can't tell from the type whether it should be quoted, or not...
Therefore, handle ids as strings, converting them to numbers when they're
fetched from the database, and back to strings as part of the queries.
This commit adds the relevant tables and code to store lint warnings in the
database.
Currently, only lint checkers which don't require access to the network will
be run, as this allows the processing to happen without network access. Also,
this functionality won't work in older versions of Guix which don't expose the
lint warnings in a compatible way.
