asp.net core 2.0 support

[mikeprince3]

I upgraded the solution to use .net core 2.0 across the board. I don't know that you'll actually want to merge this PR since you may want to keep the current master for others to use. Maybe creating a new repo or branch for it would be better. Your call for sure.

Other than updating the breaking changes, I did make a couple of updates to be aware of. I changed the port number in appsettings.json to use the default Elasticsearch port (9200) since that's what I had and what most people will have in their default setup. I have no idea about the docker support so maybe that's why you had it that way. Update as you see fit.

Another change was to add explicit dependencies to Json.net. It worked without doing this but it was showing warnings in the Dependencies section regarding a version mismatch.

I also removed all of the EntityFramework dependencies since, at least for me, more than half the reason I am using ES for identity is because I'm not using SQL and/or EF for this project. Anyway, feel free to add them back in if you'd like.

Thanks for putting together this project.

[mikeprince3]

It looks like the tests are failing but that might be something on the CI part that would have to change for 2.0. The tests all pass on my machine for what it's worth.