Connect the new viewer panel and add icon for it

novelwriter/assets/icons/typicons_light/icons.conf

@@ -59,6 +59,7 @@ maximise        = typ_arrow-maximise.svg
 menu            = typ_th-dot-menu.svg
 minimise        = typ_arrow-minimise.svg
 noncheckable    = mixed_input-none.svg
+panel           = nw_panel.svg
 proj_chapter    = mixed_document-chapter.svg
 proj_details    = typ_th-list-grey.svg
 proj_document   = typ_document-text.svg
@@ -68,7 +69,6 @@ proj_scene      = mixed_document-scene.svg
 proj_section    = mixed_document-section.svg
 proj_stats      = typ_chart-bar-grey.svg
 proj_title      = mixed_document-title.svg
-reference       = typ_at.svg
 refresh         = typ_refresh.svg
 remove          = typ_minus.svg
 revert          = typ_refresh-flipped.svg