Null no no... (Preemptively react to DI changes)

DI has been returning/proving null for services that are not registered. This is about to change. Updating EF to depend on IEnumerables for optional services and to not expect GetService to return null.
SQLite: Add some low-hanging fruit implementation

Changes include:
* Fix CreateTables & HasTables on SQLiteDataStoreCreator
* Implement SQLiteDataStoreCreator.Delete
* Update SQLiteTypeMapper.GetTypeMapping to use aspnet/DataCommon.SQLite#32
Add extension method to lookup property by storage name

Move to extension method
Airfix modeling... (Updated support for navigation fixup based on foreign keys)

Added verification of navigation fixup on materialization to monster model tests. Fixed issues with key comparisons:
- Binary keys now compared correctly
- Nullable foreign keys now interact correctly with non-nullable primary keys of the same underlying type
- Null foreign keys are handled

Also added support for 1:1 optional self-referencing relationships which required that navigations to contain information about the direction they point. Currently using the words principal and dependent for this relatively low-level API, but this could be changed if we can find more understandable terms.