Finished: Move Normal Quality logic to subclass
Created AgedBrieQualityItem

And created tests that confirm behavior.
Created SulfurasQualityItem

And test to confirm it behaves correctly.
Backstage Pass implemented

Removing duplicate/redundant tests on UpdateQuality
Added BackstagePassQualityItem with tests.
Need to update UpdateQuality() to use new subclasses
Need to implement and test CreateFromItem()
Tested/Implemented CreateFromItem()

Made UpdateQuality abstract
Confirmed all behavior works