[BUGFIX] ext_icon.gif for EXT:impexp

Every extension needs an icon, impexp too

Change-Id: I925aba612e49c392f30368136089c640a2b8198f
Fixes: #35257
Releases: 6.0, 4.7, 4.6, 4.5
Reviewed-on: http://review.typo3.org/9955
Reviewed-by: Philipp Gampe
Reviewed-by: Andy Grunwald
Tested-by: Andy Grunwald
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn