usability : document show filter input/output number and types

This issue was created automatically from an original Mantis Issue. Further discussion may take place here.

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New users often confused about WHY a filter is greyed out.

It would be very helpful if filter input and output type number and requiredments (most of which is available from domain in servermanager xml) could be parsed and displayed somewhere. Then new users would have a clue about how to adapt their current result to make it compatible with the filter they want (point to cell/cell to point etc)

This would also be helpful for new VTK users if done at VTK level. Some people who have to refer to Doxygen page to figure out what an Algorithm does do not know enough C++ and VTK (class hierarchy, conventions - polydataalgorithm's produce polydata, FillOutputPortInformation, Constructor etc) to figure it out. Here, doxygen parsing process should figure out whatevery it can (maybe an instantiator script could run before the parser and save a file that parser can read), to make VTK easier to use.