Remove stemming override for 'permitting'

Environment Agency prefer ‘environmental permit’ and ‘environmental
permitting’ to be interchangeable
Synonym updates following unified search and best bets

Remove synonyms that are no longer needed with recent weighting
improvements or can now be handled better through best bets; also
reinstate a couple that were causing problems in the past
Merge pull request #256 from alphagov/synonyms-20140714

Synonym updates following unified search and best bets