Implemented filesystem cache, one and only (see #1415)

As I remeber @fabpot attitude to "caching" in twig, he we be against all "NullCache" "NoCache" etc classes since if will provike users to create MecacheCache RedisCache and so on )

I've tried to make the changes as small as possible.

By the way, anyone knows why travis build is failing? I have the save PHP 5.5 and these tests run just fine.