* Use default DateFormatString & IsoDateFormat is already the default.

* Add TimeSpanMillisecondsGraphType & TimeSpanMillisecondsGraphType

* Fix TimeSpanSecondsGraphType serialize

* Fix DateTime to DateTimeOffset conversion

* Add TimeSpanSecondsGraphType and TimeSpanMillisecondsGraphType to GraphTypesLookup

* Fix SchemaPrinterTests tests

* Fix RegisteredInstanceTests tests

* Fix MutationTests

* Fix SchemaIntrospectionTests

* Fix StarWarsIntrospectionTests

* Add TimeSpanMillisecondsGraphTypeTests and fix

* Fix TimeSpanMillisecondsGraphType TimeSpan parsing

* Add DateGraphTypeTests

* Remove skipped test

* Add DateTimeOffsetGraphTypeTests

* Add TimeSpanSecondsGraphTypeTests

* Remove tests no longer needed