Added in MiniExiftool support and better auto_rotate, and fixed tests

Hey @owahab, I've revised much of paperclip-ffmpeg to add in MiniExiftool for extended metadata information and also support for auto_rotate specified as portrait or landscape. Please merge this in, I'm stoked about these features.
This change of auto_rotate will break current feature, which intended to convert metadata-based rotation into actual pixel rotation.
This breakage especially impacts when transcoding iOS/Android videos for PC playback, because some PC browsers (e.g. IE) ignore rotation metadata.