As a User I want Sync to be aware of my battery charge level

We want Sync to be aware of a device's battery status and make decisions accordingly. For example, if the device is plugged in, by all means sync a new bookmark immediately to the cloud. Or when the battery charge is under a certain percentage, sync less frequently.

> I am filing this now already because I think being energy aware is a core mobile principle and should not be an afterthought.
