New Features:

Added cost types (Experience, Material, Economy);
Vault plugin (optional) can be used to implement economy;
Spawner upgrade GUI customizing, layout changing, item material swapping.

New Commands:

/sm edit - to configure spawner upgrade GUI;
/sm cost type - to change cost type;
/sm cost [place/break/stacking/eggs] - to toggle selected cost and set cost amount.

New Permissions:

spawnermeta.stacking - Allow players to stack spawners;
spawnermeta.place - Allow players to place spawners;
spawnermeta.break - Allow players to break spawners;
spawnermeta.upgrades.open - Allow players to open spawner upgrades;
spawnermeta.upgrades.buy - Allow players to buy spawner upgrades;

Design:

Changed spawner item design.