Alias list_name to dataset in entities sheet

Closes https://github.com/XLSForm/pyxform/issues/652

Why is this the best possible solution? Were any other approaches considered?

The intent is to match the user-facing language of "Entity List". We discussed some alternative column names but decided that list_name has the advantage of being consistent with the choices sheet. The meanings are slightly different but very much related.

I went back and forth on the text of error messages. At first I made them generic ("Invalid name") but then I thought that would be too hard to use. I think using "entity list" in the messages is friendlier. People who have existing forms with dataset are early adopters so hopefully are in a better position to figure out the issue if they run into the message.

I also added on case-sensitive checking of reserved entity property names.

What are the regression risks?

This area is well-tested and the change is small so I don't think there are any.

Does this change require updates to documentation? If so, please file an issue here and include the link below.

https://github.com/getodk/docs/pull/1651

Before submitting this PR, please make sure you have:

[x] included test cases for core behavior and edge cases in tests
[x] run nosetests and verified all tests pass
[x] run black pyxform tests to format code
[x] verified that any code or assets from external sources are properly credited in comments

XLSForm / pyxform