Use MvcTranslator, when available, to inject helpers

- Use the MvcTranslator service, when available, to inject view helpers.
Merge branch 'hotfix/view-helper-translator' of https://github.com/weierophinney/zf2 into weierophinney-hotfix/view-helper-translator
Merge branch 'weierophinney-hotfix/view-helper-translator'