apply 'moviecounts' changes to the homepage.

This addresses issue #443

Background:
Admins need not download all videos (for disk space issues).  We should indicate to users what content is available; we did this previously on topic pages, but not on the landing page (for performance concerns).  However, the code runs fast, and we have caching--so only need to run it once

Changes:
* Abstract view/context and template/css logic into a single place, to share across homepage.html and topic.html
* Use that logic in both homepage.html and topic.html

Testing:
* Visited the homepage and topic page with some videos; seems to work!

![image](https://f.cloud.github.com/assets/4072455/944536/80cf51cc-02be-11e3-9938-3719e72cd1df.png)