[Sprint/KiltedKoala](feat): Media modal

To do:

• Click video thumbnail to open modal and autoplay
• Get dimensions of video before modal dimensions are calculated
• Allow vid progress bar seeker to work when hovering outside player
• Video player styles
• Move video controls outside player to fill modal width
• Clean up a few variable/class names so they are meaningful
• Resolve bug where newsfeed activity messages are doubled when you click on a modal
• Media should continue to shrink along vertical axis after you hit the horiz axis min
• Tablet - touch backdrop to close modal
• Tablet - Fix overflow on vertical images in portrait orientation
• Tablet - Fix faux url actually redirecting to media page
• Tablet - handle video controls
• Get img element height/width if not already in custom_data
• Enable horizontal scrolling when window is smaller than modal
• Replace screen dimensions with hardcoded min/max values
• Fix failed tests
• Fix reminded video failure
• Make videos bigger than intrinsic size
• Fix reminded images missing permalinks/comments
• Add message/title content
• Add feature flag
• Don't allow click on unloaded video activity

Will close #1539 (closed) and #1600 (closed)