Major overhaul of "randomness" throughout.

- Nobody does `import random` anymore.

- Random numbers are gotten from `ctx.random`, which is an object
of type `Randomness` with all the convenience methods that used to
be obnoxious functions in the `formulas` module.

- Every place that was using `random.random()` to implement the
equivalent of Python3 `random.choices(seq, weights)` has been updated
to use `ctx.random.weighted_choice(seq, weights)`.

This has a functional effect, since the details of random number
generation have changed. The *statistical* effect should be small.
I do observe that Copycat is having trouble inventing the "mrrjjjj"
solution right now (even in 1000 test runs), so maybe something is
slightly broken.

copycat/formulas.py

@@ -1,25 +1,6 @@
-import math
-import random
-
 from conceptMapping import ConceptMapping
 
 
-def selectListPosition(probabilities):
-    total = sum(probabilities)
-    #logging.info('total: %s' % total)
-    r = random.random()
-    stopPosition = total * r
-    #logging.info('stopPosition: %s' % stopPosition)
-    total = 0
-    i = 0
-    for probability in probabilities:
-        total += probability
-        if total > stopPosition:
-            return i
-        i += 1
-    return 0
-
-
 def weightedAverage(values):
     total = 0.0
     totalWeights = 0.0
@@ -31,27 +12,6 @@ def weightedAverage(values):
     return total / totalWeights
 
 
-def coinFlip(chance=0.5):
-    return random.random() < chance
-
-
-def blur(value):
-    root = math.sqrt(value)
-    if coinFlip():
-        return value + root
-    return value - root
-
-
-def chooseRelevantDescriptionByActivation(workspaceObject):
-    descriptions = workspaceObject.relevantDescriptions()
-    if not descriptions:
-        return None
-    activations = [description.descriptor.activation
-                   for description in descriptions]
-    i = selectListPosition(activations)
-    return descriptions[i]
-
-
 def __relevantCategory(objekt, slipnode):
     return objekt.rightBond and objekt.rightBond.category == slipnode