Created database class.

Tidied app.py so that it only contains controller logic.
Added error handling for if number of entrants exceeds number of possible identifiers
Updated test coverage to test for all identifiers, as well as error case

web/utils.py

@@ -0,0 +1,6 @@
+def remove_common_elements(a, b):
+    """Removes the common elements from both supplied lists (in place), doesnt not return a new list"""
+    for e in a[:]:
+        if e in b:
+            a.remove(e)
+            b.remove(e)