Incorrect detector shape for downsampled signal

[hakonanes]

The detector attached to a downsampled EBSD signal is incorrectly set

>>> import numpy as np
>>> import kikuchipy as kp
>>> s = kp.signals.EBSD(np.ones((60, 50)))
>>> s.detector.shape
(60, 50)
>>> s.downsample(2, show_progressbar=False)
>>> s
<EBSD, title: , dimensions: (|25, 30)>
>>> s.detector.shape
(25, 30)

The reason is that we don't flip the shape obtained from EBSD.axes_manager.signal_shape in EBSD.downsample().

I'm fixing this in a small minor release 0.10.0.