inline-ttl: create ttl choice customization setting activity

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

@@ -0,0 +1,36 @@
+<?xml version="1.0" encoding="utf-8"?>
+<LinearLayout
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:tools="http://schemas.android.com/tools"
+    android:layout_width="match_parent"
+    android:layout_height="wrap_content"
+    android:minHeight="?listPreferredItemHeight"
+    android:orientation="horizontal"
+    android:gravity="center_vertical"
+    android:background="?selectableItemBackground">
+
+    <CheckBox
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:id="@+id/ttl_selected"
+        android:layout_margin="8dp"
+        />
+
+    <TextView
+        android:layout_width="0dp"
+        android:layout_height="wrap_content"
+        android:id="@+id/ttl_title"
+        android:layout_weight="1"
+        android:textAppearance="?android:attr/textAppearanceMedium"
+        android:textStyle="bold"
+        tools:text="One Hour"
+        />
+
+    <RadioButton
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:id="@+id/ttl_default"
+        android:padding="4dp"
+        />
+
+</LinearLayout>