Podcast social icon (#264)

* Add Podcast icon to social-media-links

Fixes #254 . The current icon being used isn't the right color yet (it's
supposed to be purple, but we don't have a specific shade yet), so it's
navy for now.  This can be fixed in the byuweb/shared-icons repository.

* Build

Author: ThatJoeMoore

components/byu-social-media-links/byu-social-media-links-common.scss

@@ -57,3 +57,7 @@
 @mixin snapchat() {
     background-image: url('https://cdn.byu.edu/shared-icons/latest/social/obfuscated/sn.svg');
 }
+
+@mixin podcast() {
+    background-image: url('https://cdn.byu.edu/shared-icons/latest/social/obfuscated/po.svg');
+}

components/byu-social-media-links/byu-social-media-links-extras.scss

@@ -44,4 +44,8 @@ byu-social-media-links:not(.byu-component-rendered) {
     > .google-plus, > [slot="google-plus"] {
         @include google-plus();
     }
+
+    > .podcast {
+        @include podcast();
+    }
 }

components/byu-social-media-links/byu-social-media-links.js

@@ -13,7 +13,8 @@ const SOCIAL_NAMES = {
     'gplus': 'Google+',
     'linkedin': 'LinkedIn',
     'rss': 'RSS',
-    'snapchat': 'Snapchat'
+    'snapchat': 'Snapchat',
+    'podcast': 'Podcast'
 };
 
 const SOCIAL_IDS = Object.getOwnPropertyNames(SOCIAL_NAMES);

components/byu-social-media-links/byu-social-media-links.scss

@@ -7,6 +7,7 @@
     @include allSocialIcons();
   }
 
+  //These all have a [slot] selector for backwards-compatibility. New icons don't need it.
   ::slotted(.facebook), ::slotted([slot="facebook"]) {
     @include facebook();
   }
@@ -45,4 +46,8 @@
     @include snapchat();
   }
 
+  ::slotted(.podcast) {
+    @include podcast();
+  }
+
 }