Install Plugins screen:

* Utilize the (currently-named) filter bar from the Add Themes screen.
* Move the upload link to the h2, also like the Add Themes screen.

see #28673.

Built from https://develop.svn.wordpress.org/trunk@29218


git-svn-id: http://core.svn.wordpress.org/trunk@29002 1a063a9b-81f0-0310-95a4-ce76da25c4cd