Automatically append '/' to buildbotURL
Freestyle: calling collect_artifacts is not needed anymore

One should now use the wrapper add_step() function which ensures the
"collect_artifacts" step is always executed last so that there's no
need to explicitly call it.
Cosmethic
slave: remove keyword arguments, force max_builds to 1
WebStatus: remove 'cancelPendingBuild' permission
master: re-use 'buildbotURL' for 'titleURL'
Cosmethic: add explanatory comments
master: add data retention and cache configuration