Improvements to the plugin information modal:

* Whitespace/braces cleanup for [29040].
* Reduce width of modal to 792px, which is the default banner size.
* Reduce banner height when screen height is smaller than 500px.
* Remove inline CSS.
* Re-use tab var in JS.
* Encode ampersands in links.

props avryl, michalzuber, ocean90.
see #27440.

Built from https://develop.svn.wordpress.org/trunk@29125


git-svn-id: http://core.svn.wordpress.org/trunk@28910 1a063a9b-81f0-0310-95a4-ce76da25c4cd