Fix exif orientation for flipped images

[MorrisJobke]

fixes #13363

Links:

• http://www.daveperrett.com/articles/2012/07/28/exif-orientation-handling-is-a-ghetto/
• Example data: https://github.com/recurser/exif-orientation-examples

cc @georgehrke @tobiasKaminsky @oparoz

Before:

After:

[georgehrke]

code changes look good, will test asap

[scrutinizer-notifier]

The inspection completed: 2 new issues

[ghost]

Refer to this link for build results (access rights to CI server needed):
https://ci.owncloud.org//job/pull-request-analyser-ng-simple/7215/
👍 Test PASSed. 👍

[oparoz]

Ah, that was simple enough :)
Works! 👍
Note to testers, you need to remove all thumbnails after applying the patch for the before and after effect

[georgehrke]

tested, works 👍