Also changes menu link to /boards/ as it now shows all boards.

Also changes menu link to /boards/ as it now shows all boards.

This also fixes the is_staff constraint, as memberships
that ended today should not give staff access anymore. This is
a particularly important case, as this is typically what happens
when memberships end 'today' and the object is saved.

The previous version did not take into account that
people could have multiple memberships that did not overlap.

They are not well fit in the committee model, and are necessary
when we migrate members.