Re #6972. Adding in ParaView's pqHelpWindow.
Re #6972. Brining back old HelpWindow implementation.
Re #6972. Fixing compile error.
Re #6972. Fixing where collection file is.
Re #6972. Fixing links for algorithms and index pags.
Re #6972. Moving files about to make way for adding an interface.
Re #6972. Moving classes to make way for backage dependencies.
Re #6972. Added registration method for the help window.

This was to get around all the wackyness of package dependencies.
This is checkpointing work before actually bringing up the help
window.
Re #6972. Adding implementation in HelpWindow.
Re #6972. First pass at using the internal help widget.
Re #6972. Removing qt-assistant as an external call.
Re #6972. Changed QHelpEngine into a static variable.
Re #6972. Changing help engine to be a transient thing.
Re #6972. Changed to forward declares.
Re #6972. Changed much of the help stuff to be QWidgets.
Re #6972. Connecting shutdown to close the window.
Re #6972. Connected the shutdown signals.
Re #6972. Removing unused function.
Re #6972. Got rid of segfault on close.
Re #6972. Clearing out doxygen warnings.