Add share button for safety numbers

Fixes #5798
Closes #5854
// FREEBIE

res/menu/verify_identity.xml

@@ -0,0 +1,8 @@
+<?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:id="@+id/verify_identity__share"
+          android:title="@string/verify_identity__share_safety_numbers"
+          android:icon="@drawable/ic_share_white_24dp"
+          app:showAsAction="ifRoom" />
+</menu>

res/values/strings.xml

@@ -565,6 +565,9 @@
     <string name="VerifyIdentityActivity_your_contact_is_running_an_old_version_of_signal">Your contact is running an old version of Signal, please ask them to update before verifying safety numbers.</string>
     <string name="VerifyIdentityActivity_you_re_attempting_to_verify_safety_numbers_with">You\'re attempting to verify safety numbers with %1$s, but scanned %2$s instead.</string>
     <string name="VerifyIdentityActivity_the_scanned_qr_code_is_not_a_correctly_formatted_safety_number">The scanned QR code is not a correctly formatted safety number verification code.  Please try scanning again.</string>
+    <string name="VerifyIdentityActivity_share_safety_numbers_via">Share safety numbers via...</string>
+    <string name="VerifyIdentityActivity_our_signal_safety_numbers">Our Signal safety numbers:</string>
+    <string name="VerifyIdentityActivity_no_app_to_share_to">It looks like you don\'t have any apps to share to.</string>
 
     <!-- KeyExchangeInitiator -->
     <string name="KeyExchangeInitiator_initiate_despite_existing_request_question">Initiate despite existing request?</string>
@@ -936,6 +939,9 @@
     <!-- verify_display_fragment -->
     <string name="verify_display_fragment__scan_the_code_on_your_contact_s_phone_or_ask_them_to_scan_your_code_to_verify_that_your_messages_are_end_to_end_encrypted_you_can_alternately_compare_the_number_above">If you wish to verify the security of your end-to-end encryption with %s, compare the numbers above with the numbers on their device. Alternately, you can scan the code on their phone, or ask them to scan your code.</string>
     <string name="verify_display_fragment__tap_to_scan">Tap to scan</string>
+
+    <!-- verify_identity -->
+    <string name="verify_identity__share_safety_numbers">Share safety numbers</string>
     
     <!-- message_details_header -->
     <string name="message_details_header__issues_need_your_attention">Some issues need your attention.</string>