Username issues

The concept of using a username in registration and logging in is a great feature, but allowing a username as short as one two or three letters is not a good idea. I think a minimum of five letters should be a good starting point. Also, an exclusion dictionary is a must where trademarked names such as Facebook, Pepsi, Nokia, Microsoft etc... should be disallowed as well as foul language. eBay ran into this issue earlier on and lost lawsuits after users started hijacking trademarked names. A good way to disallow trademarked names is to start by disallowing manufacturers names and perhaps categories as well, but an excluding dictionary is still needed. Thanks!

Thanks a lot for suggestion. This work item already exists - https://github.com/nopSolutions/nopCommerce/issues/129

Done. Please see this commit for more details