Add symptoms list with checkboxes

When adding a new entry, I would like to have the option to mark that I experienced an aura, or other symptoms. In contrast to #48 (closed), I want to tag a day as a migraine w/ aura, not just "aura only". Sometimes my migraines manifests without an aura, sometimes with. This can be a simple checkbox that is un-checked by default. Obviously this checkbox is not needed for the aura only strength.

Edit: changed title from "Add 'Experienced aura' checkbox" to "Add symptoms list with checkboxes". See comment below.