statistics: add SVG icons representing chart-types

Add a few icons representing chart type (in internal terms:
chart subtypes): bar (grouped, stacked, single), box-and-whisker,
data points, pie. These should be shown in the chart selection
box.

Yes, the "artwork" is not pretty, so see these as a placeholder.

Morover, add a "warning" icon. This icon already existed as SVG,
but was not references (its png render was).

Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>

icons/chart_bar_vertical.svg

@@ -0,0 +1,66 @@
+<?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"
+   width="100mm"
+   height="100mm"
+   viewBox="0 0 100 100"
+   version="1.1"
+   id="svg8">
+  <defs
+     id="defs2" />
+  <metadata
+     id="metadata5">
+    <rdf:RDF>
+      <cc:Work
+         rdf:about="">
+        <dc:format>image/svg+xml</dc:format>
+        <dc:type
+           rdf:resource="http://purl.org/dc/dcmitype/StillImage" />
+        <dc:title></dc:title>
+      </cc:Work>
+    </rdf:RDF>
+  </metadata>
+  <g
+     id="layer1"
+     transform="translate(0,-197)">
+    <rect
+       style="fill:#ffffff;stroke:#000000;stroke-width:0.2;stroke-miterlimit:4;stroke-dasharray:none;stroke-dashoffset:0"
+       id="rect833"
+       width="99.800003"
+       height="99.800003"
+       x="0.1"
+       y="197.10001" />
+    <rect
+       style="fill:#87aade;stroke:#000000;stroke-width:0.2;stroke-miterlimit:4;stroke-dasharray:none;stroke-dashoffset:0"
+       id="rect853"
+       width="19.799999"
+       height="46.130878"
+       x="10.1"
+       y="250.76913" />
+    <rect
+       style="fill:#87aade;stroke:#000000;stroke-width:0.2;stroke-miterlimit:4;stroke-dasharray:none;stroke-dashoffset:0"
+       id="rect855"
+       width="19.799999"
+       height="87.386894"
+       x="40.099998"
+       y="209.51312" />
+    <rect
+       style="fill:#87aade;stroke:#000000;stroke-width:0.2;stroke-miterlimit:4;stroke-dasharray:none;stroke-dashoffset:0"
+       id="rect857"
+       width="19.799999"
+       height="66.071342"
+       x="70.099998"
+       y="230.82867" />
+    <rect
+       style="fill:#87aade;stroke:#000000;stroke-width:0.2;stroke-miterlimit:4;stroke-dasharray:none;stroke-dashoffset:0"
+       id="rect2083"
+       width="19.799999"
+       height="46.130878"
+       x="10.1"
+       y="250.76913" />
+  </g>
+</svg>