Fix #2136: Update the Walkthrough to match the IDE.

While the walkthrough does warn that the screenshots may not exactly
match what a user sees, people don't read these notices, instead
focussing on the images. As a result, this commit updates all of
the screenshots of the IDE to show it as it is currently, and ensures
that they all use matching code, messages, etc. Also some minor
tweaks to the text around them to match.

Change-Id: If6ae10842fa6f726d3d1ddcada4e92de2dfa97a4
Change single- to double- quotes in walkthrough warning box.

The rest of the walkthrough uses double quotes around file names,
so this just changes the warning box to be consistent with that.

Change-Id: Ib65afeff28e4330898211f8c1842abbd485ca92f
Merge changes Ib65afeff,If6ae1084

* changes:
  Change single- to double- quotes in walkthrough warning box.
  Fix #2136: Update the Walkthrough to match the IDE.