Bug 896907: let the user preview a captured video before picking it

address review comments
Bug 900208 - Opensearch plugins don't need to be stored stringified r=kgrandon
Revert "Bug 782211 - Update Gaia with additional functionality to support Notification API."

This reverts commit 359b76d47ad2694c7237332797b818c3f5b0e53b.
Merge pull request #11202 from davidflanagan/bug896907

Bug 896907: let the user preview a captured video before picking it r=daleharvey,johnhu