Revert "Remove and readd entities if their entity id has changed"

This reverts commit 1992f20baeb4cebf083370073910d15bf23ffd86.
Revert "Use the same entity id to remove entities as used to add them (fixes #486)"

This reverts commit 101a3f9ff5a82a817df1b132f7fea7718381847b.
Manage entity ids globally instead of world based