Update Environment Agency flood rule redirects

- The Environment Agency have finalised the new URLs.
Tighten up the flood path regex

- This tightens up the first `.*` to instead just match `cy/` for the
  Welsh pages, enforces `.aspx` at the end, and captures a possible
  query string.
Make EA rules case insensitive
Redirect riverlevels home without trailing slash
Merge pull request #57 from alphagov/update_ea_flood_rules

Update Environment Agency flood rule redirects