[DOC] Rework JTourBus tour for "Creating a new Activity type"

Change-Id: I5e7bc2b9b076f59bf28a74cec7c845728d3aa021
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1579
Tested-by: Jenkins CI
Reviewed-by: Bernd Bieber <brotlee@zedat.fu-berlin.de>
Reviewed-by: Damla Durmaz <ddurmaz88@gmail.com>
Reviewed-by: Franz Zieris <zieris@inf.fu-berlin.de>