[TASK] Use name-resolution instead of strings where possible: 7

(part for EXT:frontend)

Use name-resolution with ...::class instead of strings where
possible.
(needs PHP 5.5, which is meanwhile required for master)

Change-set Iedbb896607adddce2b23ab67f990fa2296c0d1bb
first introduced usage of ::class in master. We now add it
in various more places.

Change-Id: I60e9d2f7a1883f97c9a84d35dbd6e5e403e62b4b
Resolves: #63477
Releases: master
Reviewed-on: http://review.typo3.org/34862
Reviewed-by: Alexander Opitz <opitz.alexander@googlemail.com>
Tested-by: Alexander Opitz <opitz.alexander@googlemail.com>
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>