added hint to explain the contact has read up to this point

res/values/strings.xml

@@ -274,4 +274,5 @@
     <string name="leave">Leave</string>
     <string name="contact_added_you">Contact added you to contact list</string>
     <string name="add_back">Add back</string>
+    <string name="contact_has_read_up_to_this_point">Your contact has read up to this point</string>
 </resources>

src/eu/siacs/conversations/ui/ConversationFragment.java

@@ -494,6 +494,13 @@ public class ConversationFragment extends Fragment {
 											getActivity()
 													.getApplicationContext()));
 							viewHolder.contact_picture.setAlpha(128);
+							viewHolder.contact_picture.setOnClickListener(new OnClickListener() {
+								
+								@Override
+								public void onClick(View v) {
+									Toast.makeText(getActivity(), R.string.contact_has_read_up_to_this_point, Toast.LENGTH_SHORT).show();	
+								}
+							});
 
 						}
 						break;