Split test: instrument edit events for standard editor interface

This change adds 'page-edit-impression', 'page-save-(attempt/success)',
and '(section-)edit-link-click' events to the standard (non-VE) editor
interface, mirroring the events we added to VE. This makes the event data
usable for split-test analysis.

Change-Id: I51c441d61daa18d58ca7f62a9e5f07902a099050
Merge "Split test: instrument edit events for standard editor interface"