Bug 971070: implement preview gallery for Camera app [hyunacho] r=djf,jdarcangelo

resolve merge conflicts [djf]

simplify thumbnail creation code [djf]

fix error in storage library [djf]

Fixed unit tests for Bug 971090 [jdarcangelo]
(cherry picked from commit 9ae9b275beca6f17d2f31bf638b9e384d8260376)

change event in confirm controller and cleanup in preview controller [hyunacho]
(cherry picked from commit 06bd371196c81125aa9974684a93ac9cc8d69016)

fix confirm controller test [djf]

fix review nits [djf]

when discarding state on blur in secure mode, also erase thumbnail [djf]
Merge pull request #17552 from davidflanagan/bug971090

Bug971090: implement the preview gallery feature for the Camera app r=djf,justindarc