Add Splash Potions Entity to Spawner Module

[CoWinkKeyDinkInc]

Reopens #1002 that was reverted in fa2b5bf.
This adds the ability to spawn splash potions from the XML spawner module. All CTW map makers shall rejoice I suppose.

<spawners>
    <spawner spawn-region="spawner" player-region="spawner-area" delay="2s">
        <potion duration="10" amplifier="2" damage="5">
            <effect amplifier="3" duration="60">absorption</effect>
            <effect>speed</effect>
            <effect>jump_boost</effect>
        </potion>
    </spawner>
</spawners>

[CoWinkKeyDinkInc]

Tested and working @Electroid @Pablete1234