[TYPO3-core] RFC #11309: New feature: Use CSS classes for warning/error/notes/success-section-icons in Install Tool

[Niels Pardon]

This is an SVN patch request.

Type: Feature

Bugtracker references:
http://bugs.typo3.org/view.php?id=11309

Branches:
trunk

Problem:
Currently the section-icons for warning, error, notes and success are
added as normal images through an <img>-tag.

Solution:
Let's add the icons via CSS as background images to the sections so they
are easier to replace.

Notes:
I've added a further CSS class "information" for those sections that had
the "notes"-CSS-class but didn't had an icon (those sections are called
"Just information" in the header legend).

Greets,

Niels