Reimplement --securerandom

Seeds should be reproducable without the flag passed, and unreproducable with the flag passed.
With --securerandom, generate a 9-char alphanumeric string to use to make filenames differ.

DungeonGenerator.py

@@ -1,4 +1,4 @@
-import random
+import RaceRandom as random
 import collections
 import itertools
 from collections import defaultdict, deque