I don't think there is any resource other than merely making new characters and reading the skills.
Necros no longer have summons, they have a death knight which is a strong unit that has an aura. They can summon all golems at once, and the golems have been adjusted slightly. Also, bone armor acts as a super buff mastery skill when wielding wands, and wands have had damage buffed.
In terms of the other skills, lots have been altered and changed:
-Cold mastery is +% damage.
-Static is a screen wide nova that does less damage.
-Tons of synergy changes
-Zon passives have been changed
-Can summon both shadows on the sin tree
More, just too lazy to list them all, plus I probably don't remember then.
I haven't seen a skill planner, but it's not hard to use a trainer and see how well the skills work in single player.
