Externalize missing strings.

Fixes #4158
// FREEBIE

res/layout/experience_upgrade_activity.xml

@@ -14,7 +14,7 @@
     <Button android:id="@+id/continue_button"
             android:layout_width="140sp"
             android:layout_height="wrap_content"
-            android:text="continue"
+            android:text="@string/experience_upgrade_activity__continue"
             android:visibility="invisible"
             android:layout_alignParentBottom="true"
             android:layout_centerHorizontal="true" />

res/layout/redphone_call_controls.xml

@@ -65,7 +65,7 @@
               android:textColor="#FFFFFF"
               android:textAllCaps="true"
               android:background="@color/textsecure_primary"
-              android:text="Signal Call"/>
+              android:text="@string/redphone_call_controls__signal_call"/>
 
 
     <!--

res/menu/redphone_audio_popup_menu.xml

@@ -3,14 +3,14 @@
 
     <item
             android:id="@+id/handset"
-            android:title="Handset"/>
+            android:title="@string/redphone_audio_popup_menu__handset"/>
 
     <item
             android:id="@+id/headset"
-            android:title="Headset"/>
+            android:title="@string/redphone_audio_popup_menu__headset"/>
 
     <item
             android:id="@+id/speaker"
-            android:title="Speaker"/>
+            android:title="@string/redphone_audio_popup_menu__speaker"/>
 
 </menu>

res/values/strings.xml

@@ -595,6 +595,9 @@
     <!-- device_list_fragment -->
     <string name="device_list_fragment__no_devices_linked">No devices linked...</string>
 
+    <!-- experience_upgrade_activity -->
+    <string name="experience_upgrade_activity__continue">continue</string>
+
     <!-- log_submit_activity -->
     <string name="log_submit_activity__log_fetch_failed">Could not grab logs from your device. You can still use ADB to get debug logs instead.</string>
     <string name="log_submit_activity__thanks">Thanks for your help!</string>
@@ -672,6 +675,7 @@
     <string name="redphone_call_controls__end_call">end call</string>
     <string name="redphone_call_controls__audio">Audio</string>
     <string name="redphone_call_controls__mute">Mute</string>
+    <string name="redphone_call_controls__signal_call">Signal Call</string>
 
     <!-- registration_activity -->
     <string name="registration_activity__verify_your_number_to_connect_with_signal">
@@ -1042,6 +1046,11 @@
     <!-- media_preview_activity -->
     <string name="media_preview_activity__image_content_description">Image Preview</string>
 
+    <!-- redphone_audio_popup_menu -->
+    <string name="redphone_audio_popup_menu__handset">Handset</string>
+    <string name="redphone_audio_popup_menu__headset">Headset</string>
+    <string name="redphone_audio_popup_menu__speaker">Speaker</string>
+
     <!-- Trimmer -->
     <string name="trimmer__deleting">Deleting</string>
     <string name="trimmer__deleting_old_messages">Deleting old messages...</string>