Issue #3851: Profile pictures not centered

Fixes https://github.com/diaspora/diaspora/issues/3851

Notifications:
![diaspora-bug-ui-profile-picture-1](https://f.cloud.github.com/assets/1857707/77393/701c6ba6-613a-11e2-8034-33538f0aa07c.png)

Conversations:
![diaspora-bug-ui-mobile-inbox3](https://f.cloud.github.com/assets/1857707/77460/82f2525e-613f-11e2-86b1-dc477228f5d1.png)

![diaspora-bug-ui-mobile-inbox1](https://f.cloud.github.com/assets/1857707/77458/409e3d8c-613f-11e2-8925-1cee50562e01.png)

![diaspora-bug-ui-mobile-inbox4](https://f.cloud.github.com/assets/1857707/77484/9e3b8a10-6141-11e2-9b94-9eadd1a73d56.png)

Search:
![diaspora-bug-ui-profile-search](https://f.cloud.github.com/assets/1857707/77395/7aa68750-613a-11e2-8e14-73fd8b86516a.png)