extract generic LoaderFragment superclass from KeyList

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

@@ -0,0 +1,39 @@
+<?xml version="1.0" encoding="utf-8"?>
+<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:bootstrapbutton="http://schemas.android.com/apk/res-auto"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    android:orientation="vertical">
+
+    <!--rebuild functionality of ListFragment -->
+    <LinearLayout
+        android:id="@+id/loader_progress"
+        android:orientation="vertical"
+        android:layout_width="match_parent"
+        android:layout_height="match_parent"
+        android:gravity="center">
+
+        <ProgressBar
+            style="?android:attr/progressBarStyleLarge"
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content" />
+
+        <TextView
+            android:layout_width="wrap_content"
+            android:layout_height="wrap_content"
+            android:textAppearance="?android:attr/textAppearanceSmall"
+            android:text=""
+            android:paddingTop="4dip"
+            android:singleLine="true" />
+
+    </LinearLayout>
+
+    <FrameLayout
+        android:id="@+id/loader_container"
+        android:layout_width="match_parent"
+        android:layout_height="match_parent"
+        android:visibility="gone">
+
+    </FrameLayout>
+
+</FrameLayout>