Add a default card image when no custom one exists (#23)

* Add a default card image when no custom one exists
* Add coming_soon.png source
* Use directly the svg source instead of the png raster

ram/portal/static/coming_soon.svg

@@ -0,0 +1,58 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<!-- Created with Inkscape (http://www.inkscape.org/) -->
+
+<svg
+   width="420"
+   height="226"
+   viewBox="0 0 5.8333333 3.1388889"
+   version="1.1"
+   id="svg1"
+   xmlns:xlink="http://www.w3.org/1999/xlink"
+   xmlns="http://www.w3.org/2000/svg"
+   xmlns:svg="http://www.w3.org/2000/svg">
+  <defs
+     id="defs1">
+    <linearGradient
+       id="linearGradient1">
+      <stop
+         style="stop-color:#ffffff;stop-opacity:1;"
+         offset="0.59606808"
+         id="stop2" />
+      <stop
+         style="stop-color:#f5f5f5;stop-opacity:1;"
+         offset="1"
+         id="stop1" />
+    </linearGradient>
+    <linearGradient
+       xlink:href="#linearGradient1"
+       id="linearGradient2"
+       x1="0"
+       y1="1.5694444"
+       x2="5.8333335"
+       y2="1.5694444"
+       gradientUnits="userSpaceOnUse"
+       gradientTransform="matrix(0.53809522,0,0,1.8584071,-3.1388889,0)"
+       spreadMethod="pad" />
+  </defs>
+  <g
+     id="layer1">
+    <rect
+       style="mix-blend-mode:normal;fill:url(#linearGradient2);stroke:none;stroke-width:0.801535"
+       id="rect1"
+       width="3.1388888"
+       height="5.8333335"
+       x="-3.1388888"
+       y="-2.220446e-16"
+       transform="rotate(-90)" />
+    <text
+       xml:space="preserve"
+       style="font-weight:bold;font-size:0.444444px;line-height:1.25;font-family:'Noto Sans';-inkscape-font-specification:'Noto Sans Bold';letter-spacing:0px;word-spacing:0px;stroke-width:0.0138889"
+       x="1.5366687"
+       y="1.6798887"
+       id="text1"><tspan
+         id="tspan1"
+         style="font-style:normal;font-variant:normal;font-weight:normal;font-stretch:normal;font-size:0.444444px;font-family:'Noto Sans';-inkscape-font-specification:'Noto Sans';fill:#dee2e6;fill-opacity:1;stroke-width:0.0138889"
+         x="1.5366687"
+         y="1.6798887">Coming soon</tspan></text>
+  </g>
+</svg>