Several fixes and improvements to the CME disclosure JavaScript.
Improvements to thee front matter display JS:

 * add wrapping container
 * add media query support for responsive layouts
 * use a hidden class instead of manually setting dispaly: none;
Style for hidden elements.
Fix reference to Dom.
Remove window resize handler after display is closed.
Use default button.
Remove excess whitespace.
Merge pull request #18 from gauthierm/cme-disclosure-js-fixes

Several fixes and improvements to the CME disclosure JavaScript.