Show nicer error when GPS not present for image input

[himynamesdave]

Currently when an image (or images) entered as input have no GPS, the script has a hard failure:

Traceback (most recent call last):
  File "/Users/dgreenwood/Documents/repos/trek-view/telemetry-injector/telemetry-injector.py", line 96, in <module>
    main()
  File "/Users/dgreenwood/Documents/repos/trek-view/telemetry-injector/telemetry-injector.py", line 66, in main
    create_video_from_images(images_directory, output_dir, output_vid, o_vid, framerate, metadata)
  File "/Users/dgreenwood/Documents/repos/trek-view/telemetry-injector/metadata/metadata.py", line 147, in create_video_from_images
    m = g_next['GPSDateTime'].split('.')
KeyError: 'GPSDateTime'

We should show a nicer error to user:

"One or more of your images have no GPS metadata. Please remove these and try again."