Add universal yaw controller for estimation and wake steering

[misi9170]

This PR adds a new controller to enable wind field estimation followed by wake steering or other wind farm yaw control #66 .

To enable this, various new elements are added:

• estimators/ module Add estimators module #65
• Newly configured tests (in particular, using fixtures)

I also plan to at least partially address #68 in this PR, and likely also #67 (pending discussions on how best to simulate yaw controllers).

Still to do:

• Enable yaw angles to be computed as offsets in wake steering controllers and estimators Enable wind farm yaw control in various configurations #68
• Add some sort of basic (but not trivial) estimator Consensus/spatial averaging #8
• Add testing (ongoing)
• Add documentation
• Add or update example
• Complete refactor of tests to use fixtures Moved to Use test fixtures and conftest.py #82

@ejsimley tagging you here so that you can keep an eye on developments.

[misi9170]

Applying on-hold label until #82 is merged.

[misi9170]

Well, that didn't last long :) Removing on-hold label now that #82 is merged.