Added snippet pagination

__Tasks:__

- [x] test coverage
- [ ] gather feedback for my changes

__Informations:__

| Q             | A
| ------------- | ---
| Tests pass?   | yes
| Fixed tickets | none
| BC Breaks     | none
| Doc           | none
As far as I can see you are using `$this->getSnippetsQuery` for both methods, so you are loading the same data twice (once with a limit and once without). If you don't optimize the `getSnippetsAmount`-query in some way, it doesn't make any sense to me to query the database twice. Or am I missing the optimization for the amount?