USB external import, and filter chips on health-dot cards

plugins/usb/models/usb_device.py

@@ -133,6 +133,10 @@ class USBCheckout(BaseModel):
     checkoutreason = db.Column(db.Text, nullable=True, comment='Reason for checkout')
     checkinnotes = db.Column(db.Text, nullable=True)
     waswiped = db.Column(db.Boolean, nullable=True, comment='Was device wiped after return')
+    # Nullable, and never defaulted to False: a checkout with no recorded scan
+    # is one where nobody wrote it down, not one where the drive went unscanned.
+    scannedviruses = db.Column(db.Boolean, nullable=True,
+                               comment='Was the device virus-scanned on return')
 
     # Relationships
     device = db.relationship('USBDevice', backref=db.backref('checkouts', lazy='dynamic'))