Finish adding user creation to admin screen.

src/WebInterface.h

@@ -39,6 +39,7 @@ public:
     void skipVoteUpdateFromServer(User userVoting, bool forSkip);
     void voteNextSongFromServer(User userVoting, AudioTrack trackVoted);
     void voteNextPollClosedFromServer(AudioTrack winner);
+    void createUser(Wt::Dbo::Session* session, std::string username, std::string rawPassword, bool isAdmin);
     User currentUser;
 private:
     struct internal;