Add a script to interpolate direction based on GPS EXIF tags prior to upload

When using a camera or an actioncam that produces geotagged images without a `GPSImgDirection` tag it would be nice to be able to simplify and shorten the online editing/review process by pre-interpolating the photographs direction prior to upload.

This script will interpolate the direction of all images with EXIF GPS location information in a directory, the last image gets the same direction as the second to last, images with incomplete or missing location information are skipped.

see also: mapillary_issues/issues#397