As discussed in yesterday's stand-up, we will not allow viewers to access the pad for now. Reasoning is:

1. A viewer can add a viewer to a document by sharing it, so it could bring in some unwanted editors
2. Such a feature may rely on the etherpad time-slider, whose impact is currently unknown, but has reported to result in instability, such as pounding on the back-end storage and pegging the CPU of the etherpad server 

We should disable the etherpad time-slider until we are more familiar with its impact on the system.