Release 247 - WIP summon entity code migration

WIP summon entity code migration

It has been over a month since the last update, and in that time a lot of work has been done to migrate the summon mob code base to the main code base. This is a work in progress update, so nothing to actually show yet, so if all goes well there should be no noticeable changes.

There is a lot of overlap between the item and entity generators, and this change will allow for a lot of improvements to both generators, as well as a more unified experience.