Closes #308 - Display if username is taken while typing it on sign-up

Displays if the username is taken while the user is typing in the name on the sign-up form. Connects to the webmaker authentication client to determine this.
It's good practice to always include a newline in files.  The reason people do it is so that any tool that concats files together won't have one file end and another start on the same line.  If you just always do it, you'll never get burned by this.