Transfer of old Space implementation for archive purposes.

* Add the old Space implementation
* Add the SpacePool
* Change some member names of EntityPool
First version of new Space implementation

* Space is a list of unique entity IDs
* entities are only added by their IDs to lower dependencies
* IDs can be added and removed
* IDs can be extracted by passing a filter
* Forms now have a fixed instance of the Space object
* temporary spaces can be acquired via the SpacePool