Updates training/camera/photobasics.jd with FileProvider details

As of Android N, passing file:// URIs across package boundaries
throws a FileUriExposedException. This has caused frustration among
app developers trying to use our example as boilerplate code. This
patch replaces the "take picture" example with one that uses
content:// URIs and FileProvider instead.

Bug: 27636012
Change-Id: I9f0b4d9bbcd6b4bfa770dd1e4ad37f321e22195f