[TASK] Group excludefields by table

Do not display table name redundantly for each item but group items like
it is done for other fields like page types.

* Add header for each table of items in excludefields array and remove
table from item label
* Add possibility to set icon for headers
* Unset icon for page type headers
* Remove unused variable $descr

Change-Id: I2115f154ee61c00dbe5af0fc45391bae9170ce16
Resolves: #34098
Releases: 4.7,4.6,4.5
Reviewed-on: http://review.typo3.org/9108
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer
Reviewed-by: Soren Malling
Tested-by: Soren Malling
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Tolleiv Nietsch
Tested-by: Tolleiv Nietsch