[Paraview] Gradient filters

[Utkarsh Ayachit]

> Rather than fix this
> specific instance, it might be better to have a smarter output window that
> recognizes when a message is repeated and reports only once with an
> indicator of how many times it was raised. Now that I think about it, it
> would be nice if the output window also cleaned up all messages to hide some
> of the diagnostic information that comes with every message (like file
> location). That would make warnings/errors more helpful in general.

Interesting coincidence: over the Christmas break, as a fun project
for the break, I was thinking of working on refactoring ParaView's
output window to borrow ideas from Chrome's console/output window
which allows for nice formatting as well as grouping of repeated
messages etc. I never got around to actually implementing it, however
:). I just had a discussion with Dan. He'll work on putting up a
design page to collect some of the targeted features.