Bug 1002575 - Part 1: Expose client lastModified in TabsAccessor. r=rnewman
Bug 1002575 - Part 2: Display "Last synced" time in Synced tabs panel. r=rnewman

For the resources, I kept the client/last_synced (group) text sizes the
same as the tab/url (child) text sizes; and I kept the group height the
same as the child height (since I didn't want to calculate the new group
size); and I stripped the (unnecessary) backgrounds.