Image rotation

[Azaziah]

Sometimes there are images that are upside-down, would be great if they could be rotated in OpenLP.

[Zacc D (zacc-drake)]

It seems that OpenLP doesn't read EXIF rotation data.
This causes images that have been rotated elsewhere, or taken on a mobile device, to not display as expected.

OpenLP needs to be able to read this roation info I think.

Also, having a rotate button would be helpful.

[Benjamin Davies (bend1010)]

I believe that this is an important feature as people expect to be able to correctly display images taken directly from their phones.

At our church, we have encountered this bug at least twice, and we have had to use the system photo viewer instead. This is not seamless and is unnecessarily complicated.

This appears to be a problem with QtGui.QImageReader not reading the image rotation data. I have found an explanation of how the data works here: [https://www.impulseadventure.com/photo/exif-orientation.html].

A possible fix would be to rotate the images in `openlp\core\lib\__init__.py` when they are first loaded, possible using `QPainter.rotate()`. You would need to include the fix in both the `create_thumb` and `resize_image` functions.