[TASK] Render extension icons in EM directly

To increase performance of building the extension list the icons are
rendered directly instead of using an image viewhelper. The height is
corrected using CSS.

Change-Id: I60ddbdf409ed67a668f556cdcbc01799097a8109
Resolves: #53627
Releases: 6.2
Reviewed-on: https://review.typo3.org/25393
Reviewed-by: Ernesto Baschny
Tested-by: Ernesto Baschny
Reviewed-by: Nicole Cordes
Tested-by: Nicole Cordes