Dark Knigh needs some changes

[Shurrikhan]

Lazy fix -
Reduce all mp costs by 1/2

Unless you want an even lesser portion of Edges to be used outside of 2-minute buffs, it makes more sense to instead double our MP generation.

Decreasing MP costs and increasing MP generation equally allow for more MP spenders, but...

The lower the MP cost with same generation, the more "charges" bankable (3.33 -> 6.67 for 50% less cost) and charge time bankable (e.g., needing 2 edges outside of burst -> only needing 1).

The greater the MP generation at same MP costs, the lower the amount of charging time bankable (spreading the added casts more towards your otherwise especially dull between-bursts periods).