Support Android themed icons

See #77

android/app/src/main/res/drawable/ic_launcher_monochrome.xml

@@ -0,0 +1,12 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="108dp"
+    android:height="108dp"
+    android:viewportWidth="465.7143"
+    android:viewportHeight="465.7143">
+  <group android:translateX="69.85714"
+      android:translateY="69.85714">
+    <path
+        android:pathData="m245.791,150.134c0,0 -15.15,-57.931 -82.8,-50.128 0,0 -13.881,-15.037 -29.486,-14.923a28.676,28.676 0,0 1,5.909 21.949l-63.384,-50.7 38.315,66.622 -39.485,67.778 18.218,18.222h22.725l2.67,-2.5c0,0 -2.67,-22.555 22.062,-28.577 5.606,-1.364 30.509,-2.443 33.975,-26.74 0,0 15.813,23.179 -12.708,37.648 0,0 26.078,3.124 36.209,13.938 0,0 27.952,-61.491 -30.755,-84.443 0,0 52.249,-9.583 59.6,49.465 1.97,15.7 -0.89,40.545 -8.9,55.468 0,0 14.146,20.283 11.684,46.455 -0.003,0.001 34.429,-61.377 16.151,-119.534zM140.691,145.21c0,0 -7.007,12.366 -20.964,13.029 0,0 17.044,-16.457 22.062,-28.236l-3.427,13.275c0,0 -0.345,2.276 2.325,1.932z"
+        android:fillColor="#ffffff"/>
+  </group>
+</vector>

android/app/src/main/res/mipmap-anydpi-v26/ic_launcher.xml

@@ -2,4 +2,5 @@
 <adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
     <background android:drawable="@color/ic_launcher_background"/>
     <foreground android:drawable="@drawable/ic_launcher_foreground"/>
-</adaptive-icon>
+    <monochrome android:drawable="@drawable/ic_launcher_monochrome"/>
+</adaptive-icon>