Added dark icon coloured theme as well

nw/assets/icons/typicons_colour_dark/minus.svg

@@ -0,0 +1,56 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<svg
+   xmlns:dc="http://purl.org/dc/elements/1.1/"
+   xmlns:cc="http://creativecommons.org/ns#"
+   xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
+   xmlns:svg="http://www.w3.org/2000/svg"
+   xmlns="http://www.w3.org/2000/svg"
+   xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd"
+   xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape"
+   inkscape:version="1.0rc1 (09960d6f05, 2020-04-09)"
+   sodipodi:docname="minus.svg"
+   id="svg5204"
+   viewBox="0 0 24 24"
+   height="24"
+   width="24"
+   version="1.2">
+  <metadata
+     id="metadata5210">
+    <rdf:RDF>
+      <cc:Work
+         rdf:about="">
+        <dc:format>image/svg+xml</dc:format>
+        <dc:type
+           rdf:resource="http://purl.org/dc/dcmitype/StillImage" />
+      </cc:Work>
+    </rdf:RDF>
+  </metadata>
+  <defs
+     id="defs5208" />
+  <sodipodi:namedview
+     inkscape:current-layer="svg5204"
+     inkscape:window-maximized="1"
+     inkscape:window-y="0"
+     inkscape:window-x="0"
+     inkscape:cy="12"
+     inkscape:cx="12"
+     inkscape:zoom="38.125"
+     showgrid="false"
+     id="namedview5206"
+     inkscape:window-height="1344"
+     inkscape:window-width="2560"
+     inkscape:pageshadow="2"
+     inkscape:pageopacity="0"
+     guidetolerance="10"
+     gridtolerance="10"
+     objecttolerance="10"
+     borderopacity="1"
+     bordercolor="#666666"
+     pagecolor="#ffffff"
+     inkscape:document-rotation="0" />
+  <path
+     style="stroke-width:1.25;fill:#d64848;fill-opacity:1"
+     inkscape:connector-curvature="0"
+     id="path5202"
+     d="M 19.5,9.5 H 4.5 C 3.12,9.5 2,10.62 2,12 c 0,1.38 1.12,2.5 2.5,2.5 h 15 C 20.88,14.5 22,13.38 22,12 22,10.62 20.88,9.5 19.5,9.5 Z" />
+</svg>