Plugins: Add skeleton for new ExtensionManager plugin

This initial commit is merely a mockup of a ExtensionManager concept.

Change-Id: I19b2285667678a86097c043cc27a554545559eff
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>
Reviewed-by: hjk <hjk@qt.io>

src/tools/icons/qtcreatoricons.svg

@@ -645,6 +645,14 @@
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      id="backgroundRect"
      style="display:inline;fill:#ffffff" />
+  <use
+     x="0"
+     y="0"
+     xlink:href="#backgroundRect"
+     id="backgroundRect_32"
+     width="100%"
+     height="100%"
+     transform="matrix(2,0,0,2,0,-492)" />
   <use
      x="0"
      y="0"
@@ -3741,6 +3749,43 @@
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          id="lockbody-1" />
     </g>
+    <g
+       id="src/plugins/extensionmanager/images/packsmall">
+      <use
+         x="0"
+         y="0"
+         xlink:href="#backgroundRect_32"
+         id="use2597"
+         transform="translate(32,28)"
+         width="100%"
+         height="100%" />
+      <path
+         id="path6795"
+         d="m 16,423.5 v 11 M 26,418 16,423.5 6,418 m 0,11.5 10,5.5 10,-5.5 v -11 L 16,413 6,418.5 Z"
+         style="fill:none;stroke:#000000;stroke-width:2;stroke-linejoin:round"
+         sodipodi:nodetypes="cccccccccccc" />
+    </g>
+    <g
+       id="src/plugins/extensionmanager/images/extensionsmall">
+      <use
+         x="0"
+         y="0"
+         xlink:href="#backgroundRect_32"
+         id="use2600"
+         transform="translate(64,28)"
+         width="100%"
+         height="100%" />
+      <path
+         id="path4530"
+         style="fill:none;stroke:#000000;stroke-width:2;stroke-linejoin:round"
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+         id="path4682"
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+    </g>
   </g>
   <g
      inkscape:groupmode="layer"
@@ -8501,6 +8546,48 @@
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          inkscape:connector-curvature="0" />
     </g>
+    <g
+       id="src/plugins/extensionmanager/images/mode_extensionmanager_mask">
+      <use
+         x="0"
+         y="0"
+         xlink:href="#backgroundRect"
+         id="use2"
+         transform="matrix(2.125,0,0,2.125,102,-552.5)"
+         width="100%"
+         height="100%" />
+      <g
+         id="g12500"
+         style="fill:none;stroke:#000000;stroke-width:2"
+         transform="translate(1,1)">
+        <rect
+           id="rect5239"
+           width="6"
+           height="6"
+           x="75"
+           y="381"
+           ry="1.5" />
+        <use
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+           y="0"
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+           id="use6202"
+           transform="translate(12)"
+           width="100%"
+           height="100%" />
+        <use
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+           y="0"
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+           id="use6284"
+           transform="translate(0,12)"
+           width="100%"
+           height="100%" />
+        <path
+           id="path12068"
+           d="m 90,392 v 8 m -4,-4 h 8" />
+      </g>
+    </g>
     <g
        transform="translate(-595,297)"
        style="display:inline"