Enum type for entity level type/name

[vreuter]

We have the notion of "project"-level and "sample"-level entities and operations. Right now, some of the behavioral and messaging differences for these concepts are controlled through passing the strings "sample" or "project" to toggle between the two. This should be better formalized at the type level with an enum type to disambiguate, which would likely allow better editor hints and type annotation / checking.

[donaldcampbelljr]

This could be tackled along with the pipestat refactoring.

[donaldcampbelljr]

Ok, I added this enum and did some refactoring for the upcoming 1.8.0 release.