Replaces map(lambda k: …) with way faster list comprehensions.

According to timeit, it's 4 times faster for small lists (3 items)
and 20 % faster for huge lists (15000 items).
Tiny optimizations.
dict.iteritems > dict.items for Python 3.
Avoids a mutable object in a function parameter.
Removes an unused util.
Converts unpickle to a static method.
Moves a statement outside of a try…except block.
Fixes a potential bug.
Adds FIXMEs and removes unused imports in stats/views.py.
Merge pull request #46 from BertrandBordage/master

Small optimization & cleanups + fixes a potential bug.