Removed faulty upgrades in examples/usersguide/mashups.vt

Ticket: 906
Fixes typo in docs
Adds missing tag "contour 4" to mashups.vt
Usersguide: Use "contour 3" in mashups example
Fixes VisTrails messages hitting the root logger

New IPython version might set up a root logger. Its StreamHandler would
thus handle VisTrails messages alongside our own handlers.