DOP-3265: Update illustrations and icons (#98)

* changed two icons and hero image

* added new hero illustration

* deleted output.zip

Author: mmeigs

source/images/homepage-hero.png

@@ -28,7 +28,7 @@ Welcome to the MongoDB Documentation
    Find the guides, samples, and references you need to use the database,
    visualize data, and build applications on the MongoDB data platform.
 
-.. image:: /images/homepage-hero.png
+.. image:: /images/homepage-hero.svg
    :class: hero-img
    :alt: Homepage illustration
 
@@ -126,7 +126,8 @@ Community.
       :headline: Free Online Courses on MongoDB University
       :cta: Get started on MongoDB University
       :url: http://university.mongodb.com/?tck=docs_landing
-      :tag: University
+      :icon: /images/icons/university.svg
+      :icon-alt: MongoDB University icon
 
       Build your MongoDB expertise for free with in-depth lessons and
       videos on University.
@@ -135,7 +136,8 @@ Community.
       :headline: Collaborative Community Forums
       :cta: Join our Community
       :url: https://community.mongodb.com/?tck=docs_landing
-      :tag: Community
+      :icon: /images/icons/ask-the-experts.svg
+      :icon-alt: MongoDB Ask The Experts icon
 
       Learn and build relationships with like-minded developers using
       MongoDB.