Register parent service locator in servlet context, closes JERSEY-2704

Hello Jersey Team,

This is pull request to cover enhancement described in [JERSEY-2704](https://java.net/jira/browse/JERSEY-2704) and #123. This one is for ```2.14-SNAPSHOT```, contains both implementation and integration test module.

Please take a look into the code. I tried to document it well, but I'm for your disposition in case of any questions.