Expanding milestone selector to include milestones in the last 7 days

The current milestone search logic looks for the currently-active milestone. This works the weekly updates for most weeks where there is only one milestone active at a time, but gives unexpected results in a week when the milestone changes.

Since our milestones change on a Thursday and our weekly reports run for a full 7 day cycle, usually ending on a Sunday evening, we need to include any milestone active within the last 7 days or we miss data points.

This MR expands the milestone selector to do this. It also adds ordering in so that usage of project.milestones.nodes.first elsewhere in the codebase still function.