Folding status

Add "unfolded" to the __repr__ string when the Signal is unfolded e.g.:


    >>> s = signals.EDSSEMSpectrum(np.random.random((2,3,4)))
    >>> s
    <EDSSEMSpectrum, title: , dimensions: (3, 2|4)>
    >>> s.unfold()
    >>> s
    <EDSSEMSpectrum, title: , unfolded dimensions: (6|4)>