make it possible to influence output type of \OC_Image
always output a png
don't change mimetype of whole image object
remove image/pjpeg from OC_Image::_output
OC_Image::_output() - throw exception instead of falling back to png
fixing PHPDoc
unit tests for specific image type output added
Merge pull request #7728 from owncloud/oc_image_show_save_custom_mime

make it possible to influence output type of \OC_Image