Fix leveler regex failure cases

[Gavin-Bowers]

Leveler regex pattern would fail to match or have incorrect groups on cards with empty level abilities (Lighthouse Chronologist) and cards with newlines in level abilities (Kargan Dragonlord). This fix replaces the pattern with one that handles these cases. In the case of an empty ability, the group now contains an empty string. The leveler template will still need to be changed for the placeholder text not to show up on cards with empty level abilities.

[Gavin-Bowers]

I fixed the regex pattern since I accidentally committed an unfinished version originally. I also added a fix for rendering cards with empty abilities, by making middle_text return a space instead of an empty string when the regex group is empty. I tested it this time to make sure the changes work