Ocean density must be referred to as a reference density

[glwagner]

For detail-oriented folks, the variable

https://github.com/CliMA/CLIMAParameters.jl/blob/f779db6fa86f0bfce9de4ee31757fed1fe8b75ed/src/Planet/planet_parameters.jl#L36

is somewhat stressful, as the ocean density is not constant.

This quantity is really a reference density that must be defined as part of the Boussinesq approximation; it's important to identify it as a "reference" (and therefore a parameter) rather than an absolute value.

It's appropriate to include this parameter here, because it ends up appearing in a few unrelated places in ocean codes (and also user's scripts). But I think it should be called ocean_reference_density so as to not cause unwarranted stress for users that want to carefully manage their science.

[charleskawczynski]

Sounds like a good idea. In the atmosphere, we append ref (e.g., T_min_ref) to indicate reference values.

[glwagner]

For sure. That can work for mathematical notation form. Going along with #41 I think we should use the literal word reference to indicate reference values for English variable names.