Use separate menu title strings for insecure/secure calls

Fixes #4579
Closes #4580
// FREEBIE

res/menu/conversation_callable_insecure.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <menu xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto">
 
-    <item android:title="@string/conversation_callable__menu_call"
+    <item android:title="@string/conversation_callable_insecure__menu_call"
           android:id="@+id/menu_call_insecure"
           android:icon="?menu_call_icon"
           app:showAsAction="ifRoom" />

res/menu/conversation_callable_secure.xml

@@ -2,7 +2,7 @@
 <menu xmlns:android="http://schemas.android.com/apk/res/android"
       xmlns:app="http://schemas.android.com/apk/res-auto">
 
-    <item android:title="@string/conversation_callable__menu_call"
+    <item android:title="@string/conversation_callable_secure__menu_call"
           android:id="@+id/menu_call_secure"
           android:icon="@drawable/ic_call_secure_white_24dp"
           app:showAsAction="ifRoom" />

res/values/strings.xml

@@ -996,7 +996,10 @@
     <string name="push_directory__menu_refresh">Refresh contact list</string>
 
     <!-- conversation_callable_insecure -->
-    <string name="conversation_callable__menu_call">Call</string>
+    <string name="conversation_callable_insecure__menu_call">Call</string>
+
+    <!-- conversation_callable_secure -->
+    <string name="conversation_callable_secure__menu_call">Signal call</string>
 
     <!-- conversation_context -->
     <string name="conversation_context__menu_message_details">Message details</string>