#681 - Add info about Gravatar to the site

Adds a notice about Gravatar to Register and Edit Profile pages.

Screenshots:
![S1](https://f.cloud.github.com/assets/7574/319695/dea6e4a2-98d5-11e2-808a-65b1709066fa.png)
![S2](https://f.cloud.github.com/assets/7574/319696/dfa64d3e-98d5-11e2-90a0-4513c937f9e5.png)