UpdatePipeline tests (with EF6 comparison)

Removing previous 'PocoCUD' tests that were ported from EF6 test suite
Replacing with UpdatePipeline tests that better represent recommended coding patterns
Adding EF6 equivalent of the new tests (for comparison)
Introduce ability in core framework to control which part of test is measured

I've favored 'writing code like a real app' rather than trying to factor things for a lot of code/database re-use. 

Some rough results from my laptop:

Test | EF6 | EF7
------------ | ------------- | -------------
Insert 1000 entities | 2381 ms | 524 ms
Update 1000 entities | 348 ms | 261 ms
Delete 1000 entities | 3670 ms | 151 ms
Mixed 1000 entities | 2854 ms | 364 ms

I haven't dug too much into the numbers yet, I suspect most of the big differences are batching in EF7. The comparison still seems appropriate though since this is the out-of-the-box perf you get for the same code/scenario.

Obviously we can add more tests to isolate particular parts of the stack to compare. These tests are designed to hit simple high level scenarios.
Per 027c488, you'll need to remove these and install the `xunit` package via plain-old-NuGet.