Support for adaptive icons (#1095)

* Moved launcher icons from drawable to mipmap

* Added alternative drawable resource

* Added background and foreground layers

* Changed refernce in manifest to mipmap

* Updated background

app/src/main/AndroidManifest.xml

@@ -20,7 +20,7 @@
     <application
         android:allowBackup="false"
         android:fullBackupContent="false"
-        android:icon="@drawable/ic_launcher"
+        android:icon="@mipmap/ic_launcher"
         android:banner="@drawable/banner"
         android:label="@string/app_name"
         android:theme="@style/Theme.Syncthing"

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="@mipmap/ic_background"/>
+	<foreground android:drawable="@mipmap/ic_foreground"/>
+</adaptive-icon>