Make UI changes in the Simulation View for adapting the color gradient

in the Feedrate color scheme. Due to the travel speed is normally very
high compared with the other speeds in the model, the gradient is now
gradual instead of linear in order to show more changes in the low
values and less changes in the high values.
Adapt also the button styles and themes' colors.
Set the play/pause button to the left and reduce the size.

plugins/SimulationView/resources/simulation_pause.svg

@@ -1,4 +1,6 @@
 <?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#"
@@ -7,73 +9,71 @@
    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"
-   viewBox="0 0 30 30"
+   width="6mm"
+   height="6mm"
+   viewBox="0 0 5.9999999 6"
    version="1.1"
-   id="svg4620"
-   sodipodi:docname="simulation_pause.svg"
-   inkscape:version="0.92.2 (5c3e80d, 2017-08-06)">
+   id="svg877"
+   inkscape:version="0.92.2 (5c3e80d, 2017-08-06)"
+   sodipodi:docname="simulation_pause2.svg">
+  <defs
+     id="defs871" />
+  <sodipodi:namedview
+     id="base"
+     pagecolor="#ffffff"
+     bordercolor="#666666"
+     borderopacity="1.0"
+     inkscape:pageopacity="0.0"
+     inkscape:pageshadow="2"
+     inkscape:zoom="15.839192"
+     inkscape:cx="-5.3551409"
+     inkscape:cy="17.386031"
+     inkscape:document-units="mm"
+     inkscape:current-layer="layer1"
+     showgrid="false"
+     inkscape:window-width="2880"
+     inkscape:window-height="1675"
+     inkscape:window-x="-13"
+     inkscape:window-y="-13"
+     inkscape:window-maximized="1"
+     fit-margin-top="0"
+     fit-margin-left="0"
+     fit-margin-right="0"
+     fit-margin-bottom="0" />
   <metadata
-     id="metadata4626">
+     id="metadata874">
     <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>
-  <defs
-     id="defs4624" />
-  <sodipodi:namedview
-     pagecolor="#ffffff"
-     bordercolor="#666666"
-     borderopacity="1"
-     objecttolerance="10"
-     gridtolerance="10"
-     guidetolerance="10"
-     inkscape:pageopacity="0"
-     inkscape:pageshadow="2"
-     inkscape:window-width="1920"
-     inkscape:window-height="1137"
-     id="namedview4622"
-     showgrid="false"
-     showguides="true"
-     inkscape:guide-bbox="true"
-     inkscape:zoom="22.250293"
-     inkscape:cx="8.1879003"
-     inkscape:cy="12.643765"
-     inkscape:window-x="2872"
-     inkscape:window-y="-8"
-     inkscape:window-maximized="1"
-     inkscape:current-layer="svg4620">
-    <sodipodi:guide
-       position="15,15"
-       orientation="1,0"
-       id="guide4628"
-       inkscape:locked="false"
-       inkscape:label=""
-       inkscape:color="rgb(0,0,255)" />
-    <sodipodi:guide
-       position="15,15"
-       orientation="0,1"
-       id="guide4630"
-       inkscape:locked="false"
-       inkscape:label=""
-       inkscape:color="rgb(0,0,255)" />
-  </sodipodi:namedview>
-  <rect
-     style="fill:#000000;fill-opacity:1;stroke:none;stroke-width:2;stroke-miterlimit:4;stroke-dasharray:none;stroke-dashoffset:0;stroke-opacity:1"
-     id="rect5192"
-     width="2"
-     height="20"
-     x="19"
-     y="5" />
-  <rect
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-     id="rect5192-5"
-     width="2"
-     height="20"
-     x="9"
-     y="5" />
+  <g
+     inkscape:label="Layer 1"
+     inkscape:groupmode="layer"
+     id="layer1"
+     transform="translate(-11.163774,-122.8006)">
+    <g
+       id="g825"
+       transform="matrix(0.26458333,0,0,0.26458333,10.185689,121.85192)">
+      <rect
+         y="5"
+         x="19"
+         height="20"
+         width="2.7552757"
+         id="rect5192"
+         style="fill:#000000;fill-opacity:1;stroke:none;stroke-width:2.34745646;stroke-miterlimit:4;stroke-dasharray:none;stroke-dashoffset:0;stroke-opacity:1" />
+      <rect
+         y="5"
+         x="9"
+         height="20"
+         width="2.7552757"
+         id="rect5192-5"
+         style="fill:#000000;fill-opacity:1;stroke:none;stroke-width:2.34745646;stroke-miterlimit:4;stroke-dasharray:none;stroke-dashoffset:0;stroke-opacity:1" />
+    </g>
+  </g>
 </svg>