Added memoize service and use it in twig extension

__Tasks:__

- [x] test coverage
- [ ] gather feedback for my changes
- [x] submit changes to the documentation


__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | yey
| Fixed tickets | none
| BC Breaks     | none
| Doc           | https://github.com/sulu-cmf/docs/commit/a00dd076012232502e21428505e7573fed6dce2b
heh. ok I know what to call that thing now :)