Fix #264, 274, 285, 436: Add 'Losslessly rotate image' keyboard shortcuts

https://github.com/BestImageViewer/geeqie/issues/264
https://github.com/BestImageViewer/geeqie/issues/274
https://github.com/BestImageViewer/geeqie/issues/285
https://github.com/BestImageViewer/geeqie/issues/436

Additional entries on Edit/Orientation menu:
Write orientation to file
Write orientation to file (preserve timestamp)

Preferences/Metadata option "Write altered image orientation to the
metadata" must be off.
Exiftran and mogrify must be installed.