Rename "Credentials" page to "Security" for clarity (#3941)

* Rename "Credentials" page to "Security" for clarity

* Change "security" icon from cog to lock

config/locales/en.yml

@@ -200,7 +200,7 @@ en:
   applications:
     invalid_url: The provided URL is invalid
   auth:
-    change_password: Credentials
+    change_password: Security
     delete_account: Delete account
     delete_account_html: If you wish to delete your account, you can <a href="%{path}">proceed here</a>. You will be asked for confirmation.
     didnt_get_confirmation: Didn't receive confirmation instructions?

config/navigation.rb

@@ -7,7 +7,7 @@ SimpleNavigation::Configuration.run do |navigation|
     primary.item :settings, safe_join([fa_icon('cog fw'), t('settings.settings')]), settings_profile_url do |settings|
       settings.item :profile, safe_join([fa_icon('user fw'), t('settings.edit_profile')]), settings_profile_url
       settings.item :preferences, safe_join([fa_icon('sliders fw'), t('settings.preferences')]), settings_preferences_url
-      settings.item :password, safe_join([fa_icon('cog fw'), t('auth.change_password')]), edit_user_registration_url, highlights_on: %r{/auth/edit|/settings/delete}
+      settings.item :password, safe_join([fa_icon('lock fw'), t('auth.change_password')]), edit_user_registration_url, highlights_on: %r{/auth/edit|/settings/delete}
       settings.item :two_factor_authentication, safe_join([fa_icon('mobile fw'), t('settings.two_factor_authentication')]), settings_two_factor_authentication_url, highlights_on: %r{/settings/two_factor_authentication}
       settings.item :import, safe_join([fa_icon('cloud-upload fw'), t('settings.import')]), settings_import_url
       settings.item :export, safe_join([fa_icon('cloud-download fw'), t('settings.export')]), settings_export_url