Some software that spits out CSV may just quote everything, even when
not needed. Doing that prevents us from recognizing the header and
thus makes us think a file isn't in a known format.

Fixes: #11519

If we fail to find a matching driver and the file appears to be a
".csv" file, return GenericCSV as a match. This will make us try to
open the file with the generic driver and thus capture loading error
messages and show them to the user. Otherwise we would just fail to
match a driver, and report the format is unsupported, which is
confusing to a user.

Related to #11519

In order to help make more sense of why a CSV file isn't open-able,
we should log any headers we don't recognize so the user will see
them. Note that the test csv file in tests/images is from a billion
years ago, when we apparently had bank info as a column. With this,
the test that asserts we load CSV files with no errors fails on our
own sample file (!).

Related to #11519

Jamming a hundred errors into a MessageBox is not scalable and looks
pretty dumb after a few. This makes it into a proper dialog that
shows the first line of each and lets the user select each for better
readability.

Related to #11519