Added a simple validation for new app name

Currently there are no validation for app name. For example when user entered like ```Vendor;Product``` or like this ```Vendor§§Produc``` name, Laravel gives syntax error.

I added a simple validaton for this issue. And PR contains a little improvement for Composer's namespace about this issue.
Why have you added spaces between the concatenation operator. I assume laravel cs says there should be no spaces.