Plot scalebar when the axis scale have different sign

[ericpre]

Fixes #2557.

Progress of the PR

• Plot scalebar for signals with different axis scale,
• add entry to CHANGES.rst (if appropriate),
• add tests,
• ready for review.

Minimal example of the bug fix or the new feature

import hyperspy.api as hs
import numpy as np

N = 10
s = hs.signals.Signal2D(np.arange(N**2).reshape([10]*2))
s2 = s.isig[:, ::-1]
s2.plot()

Now the scale is displayed.

[codecov]

Codecov Report

Merging #2658 (db40a9e) into RELEASE_next_patch (4e56181) will not change coverage.
The diff coverage is 100.00%.

@@                 Coverage Diff                 @@
##           RELEASE_next_patch    #2658   +/-   ##
===================================================
  Coverage               76.58%   76.58%           
===================================================
  Files                     201      201           
  Lines                   29673    29673           
  Branches                 6496     6496           
===================================================
  Hits                    22724    22724           
  Misses                   5183     5183           
  Partials                 1766     1766           

Impacted Files	Coverage Δ
hyperspy/drawing/image.py	72.43% <100.00%> (ø)

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