Tidy up edition filter
Put closed and live organisations in same dropdown

makes the code simpler, as we don't need to handle two parameters.
Pass filter form action explicitly

It needs to vary depending on where the filter is used
Explicitly state default params
Use AJAX for organisation and world location featuring

Renamed .edition-filter css class to .filter-options to match the name
of the partial.
Rename AdminEditionsIndex to FilterOptions

to reflect the partial name
Fix world location cucumber feature

The filter defaults to the country being featured on, so it needs to be
explicitly cleared for one of the tests
Fix filter options test and rename