Jenkins LTS based official image

As discussed with Brian Goff - here is the official Jenkins repo for inclusion. 

Jenkins has a weekly non long-term-support release schedule - but we thought for the purposes of stackbrew we should stick to the LTS versions of Jenkins - which are infrequent enough that a pull request is feasible. 

For a logo, here is the official one in png form: https://camo.githubusercontent.com/73aa2e5efdce9c86a20922bc04f9c2bde852be4f/687474703a2f2f6a656e6b696e732d63692e6f72672f73697465732f64656661756c742f66696c65732f6a656e6b696e735f6c6f676f2e706e67 
Cool, makes sense. :+1: