VideoBlockEditor:Poster Modal

Build 1634 on 22-03-JG-fix-editor-access
360px
Reviewing disabled
Baseline History
Build 163439b1f96
Current build. There are unaccepted changes, so build 1626 is still the baseline.
Build 1581c67074a
Accepted by John Geronimo.
Build 15396c25067
Accepted by Siyang Cao.
Build 1521be7d9b9
Accepted by Tataihono Nikora.
Commenting is disabled because there's a newer build on this branch