ENH: Use a hashmap to avoid linear search for existing vtk connections
BUG: Fixed ctkVTKObjectEventsObserverPrivate::findConnection behavior for wildcards

When ctkVTKObjectEventsObserverPrivate::findConnection receives 0 parameter for an input then it cannot be used for retrieving an entry from the cache.
Then we have to do a linear search.
Merge branch 'vtkconnect-performance-improvement' of github.com:lassoan/CTK into vtkconnect-performance-improvement

Conflicts:
	Libs/Visualization/VTK/Core/ctkVTKObjectEventsObserver.cpp
ENH: Fixed Julien Finet's code review comments