Fixed charset issue while decoding token with atob

With this patch, special characters like "ö" or "ã" are properly decoded from the token. 

When the user's name has special chars, like "ö" or "ã", the keycloak.js incorrectly decodes the values without taking into consideration that they are in UTF-8. 

See https://developer.mozilla.org/en-US/docs/Web/JavaScript/Base64_encoding_and_decoding#The_.22Unicode_Problem.22