Additional fixes to new notification docs
Implemented as many of Mike's comments in cl:
https://codereview.chromium.org/12315133/
that I could, without breaking build before api moves out of experimental officially.
Also changed name of notifications.html docs to desktop_notifications and corrected
navigation to new docs both for extensions and apps.
This is in preparation for new api moving out of experimental and being named 'notifications'.
NOTRY=TRUE
Committed:
https://src.chromium.org/viewvc/chrome?view=rev&revision=186368