[TASK] Install Tool - Change default action in Standalone context

This patch moves the welcome page to a new action "about" and integrates
it into the navigation. Furthermore the default action is changed
to "importantActions" as this is the most needed action when accessing
the Install Tool.

Resolves: #67080
Releases: master
Change-Id: I8cfe7a30e57668c3ef16987d08ed7611c741e874
Reviewed-on: http://review.typo3.org/43905


Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>