Change when Mana Curve (New Deck) gets Updated

Previously, the Mana Curve was being updated every time dbListView were being updated.
Thus, on every keypress in the card search the Mana Curve was also being updated resulting in slower card search performance.

Changed the Mana Curve to being updated only when a card has been added/removed from the deck.
Merge pull request #127 from michaelb7k/Mana_Curve_Update_Fix

Change when Mana Curve (New Deck) gets Updated