[TASK] Introduce GruntJS

In order to unify build processes in the backend we introduce
GruntJS as taskrunner. It will provide a global config that takes
over the responsibility for all build processes in the future
starting with the less files of the backend skin.

Releases: master
Resolves: #65960
Change-Id: I8319300ba5fe39fd9b889ea6992275644578c563
Reviewed-on: http://review.typo3.org/38088


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Andreas Fernandez <andreas.fernandez@aspedia.de>
Tested-by: Andreas Fernandez <andreas.fernandez@aspedia.de>