Control panel cleanup

Currently, the control panel landing view (zone management) shows a list of devices with "last sync time" and "# sync sessions".  This is great on the central server!  However, since Sync sessions are not themselves syncable, these values in the data table are misleading (always 0/Never) on the distributed server.

This adds logic to show "N/A" in that case, and to unlink the "details" page where a log of sync sessions could be viewed.

Testing:
Tested for multiple servers, both with and without sync data.

Confidence:
High.  It works, a simple change.

Current page (note the blue is just me text highlighting, not actually in the HTML):
![image](https://f.cloud.github.com/assets/4072455/1102291/5486387e-180d-11e3-93ba-50ee0125ce7a.png)