Unlock more items as you play

[Binney]

To start with, the shop should only sell Seed and Nesting Material. Then as you play you should unlock more, depending on some criteria: maybe how many bird species you've found?

Needs to be balanced with the money system so you don't get locked into buying expensive food for birds that Just Don't Appreciate It

You can already access which birds have been spotted in the Journal singleton (maybe also look at how many birds have been spotted overall?)