signup: Fix the validation for login id.

Change pattern for valid login id from /^[a-zA-Z0-9_]*$/ to
/^[a-zA-Z0-9-]+([_.][a-zA-Z0-9-]*)*$/.

This allows these characters:
* hypen
* underscore and dot, but not for the first or the last character.

And this also removed some lines of code using play-jsmessages, the i18n
module for client side.
signup: Fix a mistake of the regex for validation.

* Replace * in the first group to +
* Add some tests.
Merge pull request #3 from npcode/fix-signup-validation

signup: Fix the validation for login id.