Replacing contents and images of walking papers to field papers

This PR replaces the contents of walking papers to field papers refactored from the initial work of @feyeandal.
It follows the same flow of content of the original walking papers with additional modifications because of the different workflow for generating the map atlas.

Also added is a brief mention on editing in iD and P2.

All images names are based on the original filenames since we don't have a consensus on the appropriate filename convention.

The josm plugin section was also updated to replacing WP plugin to FP plugin.