[BUGFIX] EM locallist, grouping with author

When grouping with author you may see many groups with same author. This happens
 if author of extensions is there with different email adresses.
 Further author with email is clickable which is not useful in group header.

 Solution:
 use simple groupRenderer that returns author only.

 Resolves: #M17887

Change-Id: Ia23082498fca61db975ff02eaf335578180315ea
Reviewed-on: http://review.typo3.org/1081


Reviewed-by: Björn Pedersen <bjoern.pedersen@frm2.tum.de>
Reviewed-by: Steffen Kamper <info@sk-typo3.de>
Tested-by: Steffen Kamper <info@sk-typo3.de>