Valid chars in username

[goranche]

after logging in using Google+ my username was set to "GoranBlažič", but trying to add myself to the ambassadors group failed and the following error was shown:
This value may contain only letters, numbers and @/./+/-/_ characters.

Changing the username did work, so not a huge issue

[goranche]

[jurecuhalev]

We should run it through https://pypi.python.org/pypi/Unidecode