So far this is only supported in the Suunto EON Steel backend, but we
should try to add this to others where we have such a distinction (and
maybe assign different values to the predefined libdivecomputer events).
This also adds three new icons for info, warning, and violation. The
warning icon we had already, but I drew a new one from scratch to have it
match the violation icon.
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
