add option to show redmine headers in backlogs pages

platform: 2.0.4, 2.1.5, 2.2.0 # supported: 2.0.4, 2.1.6, 2.2.1
backlogs: master # supported: 0.9.33
ruby: 1.9.3 # supported: 1.9.3, 1.8.7

so there is no visual break between the two systems. Also integrates jump-box and breadcrumbs into redmine header, if enabled.
Defaults to old behavior, setting is in the general section.