Refactored TextBox padding

Now user can pass padding value in kwargs
Value must be one of the following:
    - integer: all sides will be set to passed value
    - tuple: sides will be set in top, right, bottom, left manner (clockwise)
      if tuple length is less than 4 zeros will be appended

If user specify fixed font size bigger than available area with padding applied
font size will decreased to fit the whole string inside