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.

It also added abrief 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.