Tag fronts are now considered Section/Subsections

We've cleaned up how we handle the AdUnits for tag fronts. They are now just considered section/subsections. 

For example:
www.theguardian.com/education/universityguides
used to be
theguardian.com/education/universityguides/front
Now it is just:
theguardian.com/education/subsection

This will look funny to keywords that have a path that is different to the section. 

Like:
www.theguardian.com/news/malaysia-airlines-flight-mh17
the section is actually "world", so the ad unit will now be:
theguardian.com/world/subsection