Multimedia: Optimized the YouTube player closed captions logic
Multimedia: Used the YouTube API getIframe instead of undocumented variable
Also used clearer variable names
Multimedia: Show the duration of YouTube video on load instead of on play
Merge pull request #6033 from LaurentGoderre/improve-youtube

Improve youtube
Multimedia: Fixed the scaling of the YouTube player and Flash Fallback
Merge pull request #6034 from LaurentGoderre/improve-youtube

Multimedia: Fixed the scaling of the YouTube player and Flash Fallback
Theme/Dismissible alerts: Fixed avalanche of broken links.
Merge pull request #6036 from EricDunsworth/v4.0-broken-link-fixes

Theme/Dismissible alerts: Fixed avalanche of broken links.
Tabs: Enabled nesting of tabs

Fixes #6038
Merge pull request #6041 from pjackson28/fixnestedtabs

Tabs: Enabled nesting of tabs