[BUGFIX] Invalid rendering of high resolution icons in lists

When using high resolution icons (png) in backend modules (32x32) and
this module can be enabled/disabled in the be_groups/be_users records,
the icon is displayed bigger than desired.

This patch introduces width and height attributes in the "getIconHtml"
method to prevent this visual bug.

Resolves: #61656
Releases: master, 6.2
Change-Id: Ida484f794ab632eef8c693e41ee2b5f5d26c5e8f
Reviewed-on: http://review.typo3.org/32909
Reviewed-by: Markus Klein <klein.t3@reelworx.at>
Tested-by: Markus Klein <klein.t3@reelworx.at>