Changed roadmap/milestones.  openscholar/openscholar#3170

Instead of one big table, roadmap is one table per roadmap.
Open milestones are shown first, ascending.  Closed milestones are after that, descending by date.
Removed roadmap column (redundant)
Removed user column (confusing, esp if user was contractor)
Unlinked github.
Removed issues without a milestone.