ref(filmstrip): move vertical filmstrip overrides to new filmstrip folder

css/main.scss

 @import 'popover';
 @import 'filmstrip';
 @import 'filmstrip/filmstrip_toolbar';
+@import 'filmstrip/vertical_filmstrip_overrides';
 @import 'unsupported-browser/main';
 @import 'modals/invite/add-people';
-@import 'vertical_filmstrip_overrides';
 @import 'deep-linking/main';
 
 /* Modules END */