A change to how summons are handled

GeneralKong#3567

Currently summons are, from what I understand, set up in a way that every use of a summon spell, a unit is cached off-map, due to this one cannot have summon spells be in high numbers or else it will lag the game.

I hope this is changed, as the way it is now prevent giving too many uses to these spells, maybe have it where instead of a unit cached for each use, it caches one unit, and the spell basically copy/paste that unit.

Also, it would be great to be able to set summons to -1 uses, to enable infinite uses, like other spells.