Handle editing a manually added dive consistently

Regardless of whether the user clicks in the info tab, makes a change to
equipment or starts by editing the profile (i.e., clicking on the little
penguin), we should get into the same state and behave the same way.

This means that when editing a manually added dive we are always in
editMode == MANUALLY_ADDED_DIVE - and editMode == DIVE means we are
editing a dive that came from another source.

Fixes #379

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>