Add icons and language labels for Extension manager, titles on links.
Move text from templates to language labels.

Change-Id: If68c6481ee9bdca58b92cbb45ecba4d181b1b1b4
Resolves: #41812
Releases: 6.0
Reviewed-on: http://review.typo3.org/15499
Reviewed-by: Jigal van Hemert
Tested-by: Jigal van Hemert
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel