Fix for #356

Usernames are truncated if longer than max-width.
Using vw instead of em in caption sizes

vw allows for more responsive text design because it changes the font-size based on the size of the viewport. (1vw = 1% viewport width.)
Using vw instead of em in caption sizes

vw allows for more responsive text design because it changes the font-size based on the size of the viewport. (1vw = 1% viewport width.)
Fix for overflowing buttons in Update Videos page

This > https://i.imgur.com/NrJ28jA.png
Update video-js.css

Fallback for vw
Update video-js.css

Fallback for vw
Update khan-lite.css

Added the missing white-space property and a vertical-align hack-fix for IE6 & IE7

One more thing, since IE6 doesn't support min-height and max-height, max-height is treated as height.
Merge PR #2264 into release-0.12.0

Conflicts:
	kalite/distributed/static/css/distributed/khan-lite.css