Change Alchemist's explosive t4

[jinsediaoying]

The t4 bomb is too weak compare to t1. It is actually like a low-explosive bomb rather than a high-explsive bomb.

My idea is change it to a sustain that cost 50 to 100 mana. When actived, all the t1 bombs use 2 gems instead of one, and gain a chance to knockback.

[Sirrocco]

part of the point of the t4 bomb is to give you something else in your rotation.

[HousePet]

If its made from two alchemist gems, it should do double the gem effects.