Fix #6. You can now choose if you want to register commands or not. Added /sc clearLine to clear all the lines of the scoreboard.

You can now remove all the lines from the scoreboard by using removeLines() (#9). Removing a line or all the lines will now affect all the viewers of the scoreboard. Adding a message when you are creating a scoreboard that already exists because it could lead to a misunderstanding.

You can now rename the scoreboards and get all the viewers using the plugin API.