[TASK] Change dimension of extjs message icons from 16x16 to 32x32

This changeset just increases the width and height of the icons in
Ext.Msg based messages to make the type of the message better
noticeable.

Fabien Udriot has created the icons - thanks.

Resolves: #28772
Releases: 4.6

Change-Id: I3c3c48ec51abb50657ae3bf8f5ff7dc799b1380b
Reviewed-on: http://review.typo3.org/4154
Reviewed-by: Fabien Udriot
Reviewed-by: Xavier Perseguers
Tested-by: Xavier Perseguers
Reviewed-by: Oliver Hader