Context for 'Installed' and 'Already Installed' theme strings.

props SergeyBiryukov.
see #27889, for trunk.


git-svn-id: https://develop.svn.wordpress.org/trunk@28159 602fd350-edb4-49c9-b593-d223f7449a82
Use correct echoing context function. see #27889.


git-svn-id: https://develop.svn.wordpress.org/trunk@28160 602fd350-edb4-49c9-b593-d223f7449a82