Add HarvestProject.deleted flag to track deletions in Harvest

set this flag instead of deleting project, so we do not lose other
info about it.  can delete manually if truly unwanted

rattail_harvest/db/model/harvest.py

@@ -190,6 +190,10 @@ class HarvestProject(model.Base):
 
     updated_at = sa.Column(sa.DateTime(), nullable=True)
 
+    deleted = sa.Column(sa.Boolean(), nullable=True, doc="""
+    Flag indicating the record has been deleted in Harvest.
+    """)
+
     def __str__(self):
         return self.name or ''