Implement unicode name normalization and transliteration in order not to...

... omit accented or other non-ASCII characters from URLs. Requires unicode and unidecode.

Fixes issues:
https://github.com/opennorth/alaveteli/issues/2 
https://github.com/mysociety/alaveteli/issues/282
https://github.com/mysociety/alaveteli/issues/902

With tests. Tested and developed on ruby 1.9.1, would appreciate someone running tests on ruby 1.8.