Fix new actionbar icon sizes, rename icon to ic_launcher following Android naming conventions

OpenKeychain/src/main/AndroidManifest.xml

@@ -65,7 +65,7 @@
         android:name=".KeychainApplication"
         android:allowBackup="false"
         android:hardwareAccelerated="true"
-        android:icon="@drawable/icon"
+        android:icon="@drawable/ic_launcher"
         android:theme="@style/KeychainTheme"
         android:label="@string/app_name">
         <activity

OpenKeychain/src/main/res/layout/import_keys_qr_code_fragment.xml

@@ -33,12 +33,12 @@
             android:layout_marginTop="8dp"
             android:background="?android:attr/listDivider" />
 
-        <Button
+        <ImageButton
             android:id="@+id/import_nfc_button"
             android:layout_width="wrap_content"
             android:layout_height="match_parent"
             android:padding="8dp"
-            android:text="NFC?"
+            android:src="@drawable/ic_action_nfc"
             android:layout_gravity="center_vertical"
             style="@style/SelectableItem" />