Updated DbContext constructors to be consistent on how they handle the serviceProvider and options parameters.
Fixing build breaks
Adding ConfigurationSource parameters for InternalPropertyBuilder
Remove NullLoggerFactory
Enabled some functional tests now that end-to-end scenarios work and fixed bugs

Or: How I Learned to Stop Worrying and Love the test TODOs,

We had some functional tests that were not running waiting on Migrations support for:
* Candidate keys
* Sequences
* Default values

These are now enabled. Fixed two bugs while doing this:
* Double-dispatch was not being performed for default value SQL gen resulting in inccorect literal generation
* Not all places that needed to check for whether or not a property is a key were updated to support candidate keys.