Add tests for `/now/` endpoint

It should return 24 hours of predictions.

[#74640422]
Implement `tide-levels/now/` endpoint

- `now` queries from this moment to now + 24 hours
- Extend max number of tide levels returned to 24 hours (1440 records)

https://www.pivotaltracker.com/story/show/74640422

[Delivers #74640422]
Merge pull request #40 from sealevelresearch/tide-levels-now-endpoint

Implement `tide-levels/now/` endpoint