username/display_name/video_channel_name min length 1 and max length 50 (#1265)

username/display_name/video_channel_name min length 1 and max length 50 (#1265)

* make username, display_name and video_channel_name min length 1 and max length 50; (fixes #1263);
    ! still some bug on the frontend complains but if you remove the disabled property it creates the account just fine;
allow for usernames to start with a number;
fix test, since username can be 1 char now make test check empty;
fix test, Should fail with a too long username;
fix test, Should fail with a too small username;
fix regular expression for username and videoChannel;
change username, videoChannel to be lowercase and fix message;

* change 1 characters to 1 character