Gravatar improvements

Remove the urllib.urlopen request from rendering gravatars.  This should decrease load time because we avoid the network latency.  

**The old workflow:**
Server:
* For each gravatar:
  * Attempt to connect to connect to the gravatar url
    * If success: return <img /> with src=gravatar.url
    * If fail: create fake gravatar using name or email.

**New Workflow:**
Server:
* For each gravatar:
  * Create fake gravatar.  Set data-gravatar on the element to the gravatar url.

Client:
* On page load:
  * for each object with data-gravatar:
    * if url is not 404: replace element with img src=gravatar url.