Implemented #1162: Invoke NFC in Advanced View

- Extracted NFC code from ViewKeyActivity to NfcHelper to share code between classes
 - Changed the private anonymous Handler for NFC into a static private subclass, that uses WeakReference to avoid memory leaks
 - Added resources needed (retrieved from Graphics) for the NFC button inside ViewKeyAdvShareFragment.
 - Fixed the ripple boundary of the Share With... button to prevent it from bleeding to other buttons on the right (UX improvement)

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

@@ -99,14 +99,12 @@
             android:layout_weight="1" />
 
         <LinearLayout
-            android:id="@+id/view_key_action_key_share"
             android:layout_width="match_parent"
             android:layout_height="?android:attr/listPreferredItemHeight"
-            android:clickable="true"
-            android:background="?android:selectableItemBackground"
             android:orientation="horizontal">
 
             <TextView
+                android:id="@+id/view_key_action_key_share"
                 android:paddingLeft="8dp"
                 android:paddingRight="8dp"
                 android:textAppearance="?android:attr/textAppearanceMedium"
@@ -116,7 +114,25 @@
                 android:layout_weight="1"
                 android:drawableRight="@drawable/ic_share_grey_24dp"
                 android:drawablePadding="8dp"
-                android:gravity="center_vertical" />
+                android:gravity="center_vertical"
+                android:background="?android:selectableItemBackground"/>
+
+            <View
+                android:layout_width="1dip"
+                android:layout_height="match_parent"
+                android:gravity="right"
+                android:layout_marginBottom="8dp"
+                android:layout_marginTop="8dp"
+                android:background="?android:attr/listDivider" />
+
+            <ImageButton
+                android:id="@+id/view_key_action_key_nfc"
+                android:layout_width="wrap_content"
+                android:layout_height="match_parent"
+                android:padding="8dp"
+                android:src="@drawable/ic_nfc_grey_24dp"
+                android:layout_gravity="center_vertical"
+                android:background="?android:selectableItemBackground" />
 
             <View
                 android:layout_width="1dip"
@@ -154,6 +170,7 @@
 
         </LinearLayout>
 
+
         <View
             android:layout_width="match_parent"
             android:layout_height="1dip"