Only allow member logos to be shown

Only members should have their logos shown. This drastically reduces the number of broken images - most (all?) nonmembers have logos specified but have no logo uploaded. Only ~50 members have bad logos.

All tests pass.

![2014-10-07-095050_736x534_scrot](https://cloud.githubusercontent.com/assets/3379265/4543277/cd6d4ea0-4e29-11e4-8f72-e03999baa120.png)