Refactor, rename PATH to BASE_PATH
Add tests that tide levels/windows make 1 db query

[#76514752]
Pre-fetch `Minute` in Prediction QuerySet

This should fix the horrendous performance problem introduced by
separating out the prediction datetime into the Minute model.

https://www.pivotaltracker.com/story/show/76514752
[Fixes #76514752]
Merge pull request #60 from sealevelresearch/fetch-datetime-in-single-query

Pre-fetch `Minute` in Prediction QuerySet