data: Move contents of data/ directory to the relevant src directories

These are bits relevant to the various components of cockpit. Move them
to the src/ directories.

Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>
ws: Fix 'make install-test-assets'

Closes #579
Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>