[BUGFIX] Address reference wind height warnings raised unnecessarily

[misi9170]

#1000 introduced a warning that is raised when turbine_type is set without setting the reference_wind_height, to let users know that the reference wind height had not been updated. This was pointed out by @cfrontin and also something I ran into recently while working on other aspects of the FLORIS code.

While this works as intended, the warning is now raised in some places (particularly set_operation_model) where the turbine_type is set implicitly (without direct input from the user). This pull request addresses the unnecessary warning raised by explicitly setting the reference_wind_height (to be the same as it was) when set_operation_model is called.

I've also updated some examples to add the reference wind height when the turbine model is set, as well as the calculate_horizontal_plane_with_turbines() function (which also implicitly sets the turbine_type). The following examples are updated:

• examples_turbopark/001_...py
• examples_turbine/003_...py
  Note that examples_turbine/001_check_turbine.py also raises the warning; however, in that case, the warning is raised appropriately, and the assign_hub_height_to_ref_height() method is then called to "correct" the problem. I therefore left this example as is.

In making the fixes, I also have created a @property for the reference_wind_height at the FlorisModel level to make it easy for users to access.

[paulf81]

This looks good @misi9170 , I reviewed the code and all makes sense to me. Thanks!