Breadcrumbs display for IHasMajorHeading views

According the the current heading rules at:

https://dev.launchpad.net/VersionThreeDotO/UI/Conversion#Heading rules

for pages where the context is the root context, breadcrumbs should not display.

The url:

https://launchpad.dev/sprints/futurista

is a bit strange, in that the sprint content class does provide IRootContext, and so the heading is displayed in the watermark. Adding IMajorHeadingView to the SprintView then correctly ensures that the heading is displayed as an H1 - but the breadcrumbs still display below the application tabs. (Note, we don't normally see this, for example, for people, because there are not normally > 1 breadcrumbs, but in this case there is one for the ISprintSet and then the index.)

Barry provided a work-around for this, which was to provide a SprintIndexHierarchy which has display_breadcrumbs set to False - and this fixes the issue on the sprint index, but it also ensures that sub-pages no-longer display breadcrumbs (as in the work-around the SprintIndexHierarchy is a hierarchy view used for ISprint generally so all the sub-pages which have the same context get display_breadcrumbs == False too).

Another work-around would be to disable/remove the ISprintSet breadcrumb - I'm not sure what would be better. I'll take a look at what would be involved to fix the actual bug too.