VideoBlockEditor:Poster Modal

Build 1572 on main
1200px
Reviewing disabled
Baseline History
Build 157254ae7e1
Current build. There are unaccepted changes, so build 1559 is still the baseline.
Build 1559d2a84aa current baseline
Accepted by Tataihono Nikora.
Build 15396c25067
Accepted by Siyang Cao.
Build 1521be7d9b9
Accepted by Tataihono Nikora.
Commenting is disabled because there's a newer build on this branch