Add <hints> to all levels

[Wuzzy2]

Many levels do not have <hints> yet, this needs to change.

<hints> contains a possible solution for the level, it's used for regression testing.

[Wuzzy2]

I added hints to a couple of levels in finished in dc6e5ec.

[Wuzzy2]

Note that regression testing is still incomplete. For instance, the phone number can't be set. So a proper regression test of levels with detonator boxes might not work yet.