metrics: standalone log()

[casperdcl]

• fixes petric.QualityMetrics: call without algorithm #51

[KrisThielemans]

Actually, I'd see this more as

class QualityMetrics:
    def __call__(...) # as is in this PR
    def metrics(self, test_im):
        ret = []
        test_im_arr = test_im.as_array()
        res.append(("RMSE_whole_object", some_calc(test_im_arr)))
        res.append(("metric2", some_other_calc(test_im_arr)))             

   def log(self, test_im, iteration):
        m = self.metrics(test_im)
        # some TB stuff

That way, we can say

   metrics = QualityMetrics(reference_image, whole_object_mask, background_mask, other_VOI_stuff)
   print(metrics.compute(some_image))

and make nice plots for lots of stored images... Otherwise, it'd always go to TB, which in my mind makes my life harder (maybe it shouldn't)

[casperdcl]

@KrisThielemans better now?

[KrisThielemans]

looks great! I haven't tried it yet though, I'm assume you did. In that case, merge! Thanks a lot