Remove Set_Data() from the copy, resize/move and new dialog class APIs

The copy, resize/move and new dialog classes (Dialog_Partition_Copy,
Dialog_Partition_Resize_Move and Dialog_Partition_New respectively) had
to be used like this:

    construct dialog object passing some parameters
    call Set_Data() to pass more parameters
    run() dialog
    call Get_New_Partition()

There is nothing in the classes which forces Set_Data() to be called,
but it must be called for the dialogs to work and prevent GParted from
crashing.

Make these class APIs safer by making it impossible to program
incorrectly in this regard.  Move all the additional parameters from
each Set_Data() method to each constructor.  The constructors just call
the now private set_data() methods.