Update Session.php

Handle PHP versions < 5.4 when checking if sessions is active.
Refactor Product fixture, introduce helpers

- Refactored Product fixture removing unneeded responsibility
  and by introducing the concept of "helpers".
- Added Website helper
- Adjusted ProductSpec accordingly
- Commented CoreConfigSpec causing PhpSpec to return non-zero value
Refactor Product fixture

- Removed unnecessary constant
Refactor Website helper

- Removed unnecessary code
Refactored Website helper, Product & ProductSpec

- Added service container in Product fixture
- Added DocBlock in Website helper according to standard one
Merge pull request #49 from walterdolce/feature/refactor-product-fixture-introduce-helpers

Refactor Product fixture, introduce helpers
Merge pull request #44 from robjstanley/patch-1

Update Session.php
Fix bad method call in product fixture
Merge pull request #50 from walterdolce/hotfix/fix-bad-method-call-in-product-fixture

Fix bad method call in product fixture