inline-edit: move action mode menu handling int activity

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

@@ -0,0 +1,9 @@
+<?xml version="1.0" encoding="utf-8"?>
+
+<ImageView xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="wrap_content"
+    android:layout_height="wrap_content"
+    android:layout_centerInParent="true"
+    android:padding="0dp"
+    android:src="@drawable/ic_mode_edit_white_24dp"
+    style="@style/Widget.AppCompat.ActionButton" />