Add an new middleware: utf8-cleaner

  Removes invalid UTF8 characters from the URL and fix the exception about:

```
ArgumentError: invalid byte sequence in UTF-8
Error class: ArgumentError
Error message: ArgumentError: invalid byte sequence in UTF-8
Action: welcome#index
URL: https://acx.io/?%F6"%20onmouseover%3Dprompt(962137)%20//

/vendor/bundle/ruby/2.1.0/gems/rack-1.5.2/lib/rack/utils.rb:104 in "normalize_params"
/vendor/bundle/ruby/2.1.0/gems/rack-1.5.2/lib/rack/utils.rb:96 in "block in parse_nested_query"
/vendor/bundle/ruby/2.1.0/gems/rack-1.5.2/lib/rack/utils.rb:93 in "each"
/vendor/bundle/ruby/2.1.0/gems/rack-1.5.2/lib/rack/utils.rb:93 in "parse_nested_query"
/vendor/bundle/ruby/2.1.0/gems/rack-1.5.2/lib/rack/request.rb:373 in "parse_query"
/vendor/bundle/ruby/2.1.0/gems/actionpack-4.0.2/lib/action_dispatch/http/request.rb:321 in "parse_query"
/vendor/bundle/ruby/2.1.0/gems/rack-1.5.2/lib/rack/request.rb:188 in "GET"

```