Add "video/quicktime" as a default Video MIME type

Summary: Ref T11142. H264 video in a Quicktime container works in Safari and Firefox for me (although not Chrome), so include it in the default video mime types.

Test Plan: Uploaded video file from T11142 locally, saw it render with <video /> properly in Safari.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11142

Differential Revision: https://secure.phabricator.com/D16121