Deal with unknown instruments with the Unknown driver

Rather then rejecting them from enumeration

src/labtoolkit/Unknown/Unknown.py

@@ -0,0 +1,5 @@
+from ..instrument import Instrument
+
+class Unknown(Instrument):
+    """."""
+    pass

src/labtoolkit/__init__.py

@@ -513,6 +513,11 @@ def driver_map(self):
         self.enumeration = pd.merge(
             self.drivers, self.enumeration, how="right", on=['Manufacturer', 'Model']
         )
+        for index, inst in self.enumeration.iterrows():
+            if pd.isnull(inst['Type']) and pd.isnull(inst['Driver']):
+                self.enumeration.loc[index, 'Type'] = 'Unknown'
+                self.enumeration.loc[index, 'Driver'] = 'Unknown'
+
 
     def drivers_sorted(self):
         """."""