Seperate concerns in 'get_input_board'

[tinsmancb]

The function get_input_board is currently doing two different things that should be handled by two seperate functions:

1. Prompting the user to input a sudoku board
2. Converting a sudoku board represented as a string to a Sudoku object. This second function should not print anything or prompt for input.

The second of these should be a method of the Sudoku class! The constructor (__init__ method) should detect the type of its input with the typeof and feed it into the string conversion function if appropriate.