Rename '1D profile' methods

[anowacki]

Previously, we had a get_ method which returned the radial or 1D profile of a model at a certain point, but get_ methods are by convention those which return the data inside a model, possibly for editing. In updating this name, a simple change to 1d_profile was not possible under Python's naming rule so another name was needed. This commit changes TerraModel.get_1d_profile to TerraModel.radial_profile, and for consistency also changes TerraModel.mean_1d_profile to TerraModel.mean_radial_profile.

As an alternative I considered profile_1d, but that didn't feel right. A '1D profile' is really tautologous, since a profile is by definition 1D. Hence adding information about in which direction the profile was running seemed most useful. Finally therefore we settle on TerraModel.radial_profile as the best alternative.

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[anowacki]

@jamespanton93 I've opened this as a request for feedback. If you're happy with the changes, then I think our API is now pretty much ready.

[anowacki]

Docs build seems to have failed for an unrelated reason.