complete typeChanges.md documentation

[xmonader]

https://github.com/threefoldtech/tfchain_graphql/blob/master/docs/typeChanges.md

[DylanVerstraete]

addressed here https://github.com/threefoldtech/tfchain_graphql/pull/123

[mohamedamer453]

Verified from https://github.com/threefoldtech/tfchain_graphql/blob/master/docs/typeChanges.md

The docs were updated, and the todo sections in the docs were completed.