omnibox tutorial corrections
removed tut_browsingdata.html (dupe), and did small edit to tut_removing_browsingdata.html
fixed spelling error
privacy tutorial and api doc cleanup
contentSettings tutorial and API cleanup
added link to API docs
removed link to stash api for now.
Off-Road Mode tutorial and sample extension

Signed-off-by: Shwetank Dixit <emailshwetank@gmail.com>