Change where images are saved

[MattGrossi-NOAA]

Currently, images are saved in a new subdirectory called "images" located within the same directory that the videos are located. This is problematic for at least two reasons:

1. The videos will not always be stored locally. They may be on a server somewhere.
2. Since a given frame may contain multiple annotations, either more than one species or more than one individual of the same species, the images need to be sorted by species to differentiate between individuals.

[MattGrossi-NOAA]

Related to #2

[MattGrossi-NOAA]

Added a separate image directory to docker-compose.yml for this purpose. Also added a command line control flag for this when running outside the container, though this approach is not recommended.

This implementation needs to be tested on other file systems, so keeping this open for now.