[TASK] Make Install Tool look beautiful in modern IE's

IE9 and later understand CSS3 features which we use in the Install
Tool. Make sure IE don't fall back into IE7 mode.

Resolves: #52413
Releases: 6.2
Change-Id: I48933d44e63a59deac131a7cbfeda38fc77aafff
Reviewed-on: https://review.typo3.org/24186
Reviewed-by: Wouter Wolters
Reviewed-by: Christian Kuhn
Reviewed-by: Ernesto Baschny
Tested-by: Ernesto Baschny