Add two alternative views for positions

Previously, the position view only took a PositionTitle slug;
this change also allows you to list positions by:

 - PositionTitle slug and OrganisationKind slug
 - PositionTitle slug, OrganisationKind slug and Organisation slug
Remove an unnecessary (and non-PEP-8) newline
With the new position views, the Member role substitutions can go

The "NA Member" and "NCOP Delegate" position titles were really
a workaround for not having positions views that could select
for OrganisationKind and Organisation.  Now those are added,
the workaround can be removed.
Switch to using Member for NA and NCOP membership