[XML Monsters] Add effect support to summons tag

[EPuncker]

Current code:

	<summons maxSummons="2">
		<summon name="Hyaena" interval="1050" chance="100" />
	</summons>

Desired functionality:

	<summons maxSummons="2">
		<summon name="Hyaena" interval="1050" chance="100" radius="2" target="0">
			<attribute key="areaEffect" value="redshimmer" />
		</summon>
	</summons>

Why? So we can code different summon effects without the need of additional Lua spells, and also be able to bypass blue teleport effect as it has been already made possible with this commit: https://github.com/otland/forgottenserver/commit/76d4aa55db927f53589e52156b3bf7e122425833

PS: of course the block structure is subject to change, I added only an idea of how it would look