Add support for adaptive icons

Closes #395

app/build.gradle

@@ -6,7 +6,7 @@ apply plugin: 'com.github.triplet.play'
 
 android {
     compileSdkVersion 27
-    buildToolsVersion "25.0.2"
+    buildToolsVersion "27.0.3"
 
 //    signingConfigs {
 //        release {

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

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="utf-8"?>
+<adaptive-icon xmlns:android="http://schemas.android.com/apk/res/android">
+    <background android:drawable="@color/ic_launcher_background"/>
+    <foreground android:drawable="@mipmap/ic_launcher_foreground"/>
+</adaptive-icon>

app/src/main/res/values/ic_launcher_background.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<resources>
+    <color name="ic_launcher_background">#1976D2</color>
+</resources>