[MM-28638] Improve image thumbnail generation logic (#15534)

* Improve image thumbnail generation logic * Improve naming
2020-10-09 08:47:20 +02:00
--- a/tests/10000x1.png
+++ b/tests/10000x1.png
--- a/tests/10000x1_expected_preview.jpeg
+++ b/tests/10000x1_expected_preview.jpeg
--- a/tests/10000x1_expected_thumb.jpeg
+++ b/tests/10000x1_expected_thumb.jpeg
--- a/tests/1x10000.png
+++ b/tests/1x10000.png
--- a/tests/1x10000_expected_preview.jpeg
+++ b/tests/1x10000_expected_preview.jpeg
--- a/tests/1x10000_expected_thumb.jpeg
+++ b/tests/1x10000_expected_thumb.jpeg