Only ignore the word 'the' for orgnisation sorting

This was getting very confusing as the sort order was non-obvious and
didn't use the standard prefixes to remove before sorting. Switched it
to just ignore the word 'the'.
Group organisations in the filter lists by type

It is far clearer if the organisations in the filter list are grouped by
type so the most important ones come first. This changes the list to
first have ministerial organisations listed and then all other
afterwards.

Also added an `includes` to ensure that both translations and types are
pre-fetched to avoid n+1 queries.
Use scope rather than select and reject

Abstract away the logic involved in picking ministerial and
non-ministerial organisations.
Merge pull request #445 from alphagov/filter-input-sort

Tracker: https://www.pivotaltracker.com/story/show/45670251

Sort order of organisations on document filter pages