Simplify the SVG logo (#974)

The changes are:
- Removal of useless metadata.
- Simplification of shapes.
- Simplification of coordinates.
- Addition of a white background, to make the logo look correct on dark
  backgrounds.

logo/conversejs.svg

-<?xml version="1.0" encoding="UTF-8" standalone="no"?>
-<!-- Created with Inkscape (http://www.inkscape.org/) -->
-
-<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"
-   width="744.09448819"
-   height="1052.3622047"
-   id="svg3086"
-   version="1.1"
-   inkscape:version="0.48.5 r10040"
-   sodipodi:docname="conversejs.svg"
-   inkscape:export-filename="/home/jc/Pictures/conversejs.png"
-   inkscape:export-xdpi="90"
-   inkscape:export-ydpi="90">
-  <defs
-     id="defs3088" />
-  <sodipodi:namedview
-     id="base"
-     pagecolor="#ffffff"
-     bordercolor="#666666"
-     borderopacity="1.0"
-     inkscape:pageopacity="0.0"
-     inkscape:pageshadow="2"
-     inkscape:zoom="0.35"
-     inkscape:cx="414.68086"
-     inkscape:cy="602.54021"
-     inkscape:document-units="px"
-     inkscape:current-layer="g3569"
-     showgrid="false"
-     inkscape:window-width="1366"
-     inkscape:window-height="768"
-     inkscape:window-x="0"
-     inkscape:window-y="0"
-     inkscape:window-maximized="0">
-    <inkscape:grid
-       type="xygrid"
-       id="grid3567" />
-  </sodipodi:namedview>
-  <metadata
-     id="metadata3091">
-    <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
-     inkscape:groupmode="layer"
-     id="layer2"
-     inkscape:label="background" />
-  <g
-     inkscape:groupmode="layer"
-     id="layer3"
-     inkscape:label="stars" />
-  <g
-     inkscape:label="Layer 1"
-     inkscape:groupmode="layer"
-     id="layer1">
-    <g
-       id="g3569">
-      <path
-         style="fill:#000000;fill-opacity:1"
-         d="M 80.03125 44.53125 C 48.947058 44.53125 23.9375 69.540808 23.9375 100.625 L 23.9375 754.4375 C 23.9375 785.52169 48.947058 810.5625 80.03125 810.5625 L 664.59375 810.5625 C 695.67794 810.5625 720.71875 785.52169 720.71875 754.4375 L 720.71875 100.625 C 720.71875 69.540808 695.67794 44.53125 664.59375 44.53125 L 80.03125 44.53125 z M 93.5 56.6875 L 652.28125 56.6875 C 682.44574 56.6875 706.75 80.99176 706.75 111.15625 L 706.75 326 L 622.75 421.34375 L 135.28125 421.34375 L 125.875 429.15625 L 40.3125 528.03125 L 38.9375 377.1875 L 39.375 372.625 C 39.179137 370.73917 39.0625 368.84558 39.0625 366.90625 L 39.0625 111.15625 C 39.0625 80.99176 63.335507 56.6875 93.5 56.6875 z M 505.25 148.65625 C 455.78924 148.65625 415.6875 188.72674 415.6875 238.1875 C 415.6875 287.64826 455.78924 327.75 505.25 327.75 C 554.71076 327.75 594.8125 287.64826 594.8125 238.1875 C 594.8125 188.72674 554.71076 148.65625 505.25 148.65625 z M 235.9375 523.84375 C 236.70563 523.82429 237.47718 523.84375 238.25 523.84375 C 287.71076 523.84375 327.78125 563.91424 327.78125 613.375 C 327.78125 662.83576 287.71076 702.9375 238.25 702.9375 C 188.78924 702.9375 148.6875 662.83576 148.6875 613.375 C 148.6875 564.68707 187.54503 525.06978 235.9375 523.84375 z "
-         id="rect3211" />
-      <path
-         sodipodi:type="arc"
-         style="fill:none"
-         id="path3473"
-         sodipodi:cx="-131.42857"
-         sodipodi:cy="233.79076"
-         sodipodi:rx="5.7142859"
-         sodipodi:ry="1.4285715"
-         d="m -125.71429,233.79076 a 5.7142859,1.4285715 0 1 1 -11.42857,0 5.7142859,1.4285715 0 1 1 11.42857,0 z" />
-    </g>
-  </g>
+<?xml version="1.0"?>
+<svg xmlns="http://www.w3.org/2000/svg" version="1.1" width="744" height="852">
+ <path fill="#fff" d="M 80 44.5 C 49 44.5 24 69.5 24 100.625 V 754.5 C 24 785.5 49 810.5 80 810.5 H 664.5 C 695.7 810.5 720.7 785.5 720.7 754.5 V 100.625 C 720.7 69.5 695.7 44.5 664.5 44.5 H 80 z"/>
+ <path fill="#000" d="M 80 44.5 C 49 44.5 24 69.5 24 100.625 V 754.5 C 24 785.5 49 810.5 80 810.5 H 664.5 C 695.7 810.5 720.7 785.5 720.7 754.5 V 100.625 C 720.7 69.5 695.7 44.5 664.5 44.5 H 80 z M 93.5 56.7 H 652.3 C 682.44574 56.7 706.75 81 706.75 111.15625 V 326 L 622.75 421.34375 H 135.3 L 39 528 V 111.15625 C 39 81 63.335507 56.7 93.5 56.7 z"/>
+ <circle cx="505.3" cy="238.2" r="89.5"/>
+ <circle cx="238.2" cy="613.4" r="89.5" fill="#fff"/>
 </svg>