fix(app): add missing `contact_add.svg` icon

tests/assets/images/contact_add.svg

+<?xml version="1.0" encoding="UTF-8"?>
+<svg width="22px" height="19px" viewBox="0 0 22 19" version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
+    <!-- Generator: Sketch 40.3 (33839) - http://www.bohemiancoding.com/sketch -->
+    <title>contact_add_default</title>
+    <desc>Created with Sketch.</desc>
+    <defs></defs>
+    <g id="Symbols" stroke="none" stroke-width="1" fill="none" fill-rule="evenodd" stroke-linecap="round">
+        <g id="contact_add_default">
+            <path d="M8.54029156,2.5 C10.850165,2.5 12.7226588,4.39098325 12.7226588,6.72356259 C12.7226588,7.83995271 12.2940348,8.85494372 11.5935908,9.61033703 C11.4952898,9.71653609 11.5340928,9.69793625 11.4252454,9.79333541 L11.5997595,9.91213435 C17.938579,12.6985097 16.3132304,17.3824682 16.3132304,17.3824682 C12.2309551,18.6900566 8.54685822,18.4888584 8.54685822,18.4888584 L8.45333302,18.4888584 C8.45333302,18.4886584 4.7688382,18.6900566 0.686761802,17.3824682 C0.686761802,17.3824682 -0.938586743,12.6985097 5.40043177,9.91213435 L5.57494581,9.79333541 C5.4660984,9.69793625 5.50490141,9.71653609 5.40660046,9.61033703 C4.70635541,8.85494372 4.27753243,7.83995271 4.27753243,6.72356259 C4.27753243,4.39098325 6.15002629,2.5 8.45989968,2.5 L8.54029156,2.5 L8.54029156,2.5 Z" stroke="#FFFFFF" stroke-linejoin="round"></path>
+            <path d="M18.4166667,0.583333333 L18.4166667,6.41666667" stroke="#FFFFFF"></path>
+            <path d="M15.5,3.5 L21.3333333,3.5" stroke="#FFFFFF"></path>
+        </g>
+    </g>
+</svg>