Roadmap should warn if there are issues outside of the project scope within Epics

Summary

Currently, Simple Roadmaps can't be used cross-project. That means that issues outside the current project's scope won't be considered within the Roadmap.

But, the Roadmap won't give any warn whether or not there are issues that won't be considered, which could make users be unaware of such existing work.

Suggestion

Have Roadmap display a flag or some kind of warn when there are issues outside the scope under the Epics within the roadmap.