Put class specific class first when sorting by mana cost.

I'm not sure if the current sorting was the intended sorting but it's been bother me that when finding the specific class minion, i need to scroll down before i see the class specific minion, meanwhile all class specific spells are always on top.

For example, when editing a priest deck, for the 1 mana cost cards, this is what it looks like:

http://imgur.com/iqmKKG6,dMUJ9O7,mW8Uf9I,Qy1jayr#0

1. Holy Smite
2. Inner Fire
3. Mind Vision
4. Power Word: Shield
..... (neutral 1 mana cost minions)
17. Northshire Cleric

this PR make the list sorted as this:

http://imgur.com/iqmKKG6,dMUJ9O7,mW8Uf9I,Qy1jayr#3

1. Holy Smite
2. Inner Fire
3. Mind Vision
4. Northshire Cleric
5. Power Word: Shield
..... (neutral 1 mana cost minions)

For the 2 mana cost for priest, this is the before:

http://imgur.com/iqmKKG6,dMUJ9O7,mW8Uf9I,Qy1jayr#1

and after:

http://imgur.com/iqmKKG6,dMUJ9O7,mW8Uf9I,Qy1jayr#2