[TASK] Load bootstrap datetimepicker via bower

The Bootstrap DateTimePicker library previously located in
"typo3/contrib/twbs" is now fetched via bower and copied
to the public JavaScript folder via Grunt.

The LESS inclusion path is modified as well.

Resolves: #66076
Releases: master
Change-Id: Iea302310f59d729c4c16012bc572e9471e2c433e
Reviewed-on: http://review.typo3.org/38285


Reviewed-by: Jan Helke <typo3@helke.de>
Tested-by: Jan Helke <typo3@helke.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>