restructured, generalized and renamed VtkSelectionFilter (now: VtkAppendArrayFilter); selected elements in MshView are now highlighted in render window; fixed issues with geo object selection (list items hadn't been recognised properly)
moved initial radius calculation if various filters to CompositeFilter parent class
added mesh-element-view class and started implementing hightlighting of selected mesh nodes
the element model is now updated by selecting an element in the mesh view, selection-indix parameters for various signals and methods have been unfied to unsigned
split up selection filter into node-selection and element-selection; node selection is working now
added vtkSmartPointer to selection filters for memory management
Corrected highlighting in 3d view.
Better doxygen comments.

This fixes #37.
fixed an issue that would cause a crash upon right-clicking a mesh element
removed remaining debug code
Merge pull request #127 from rinkk/MeshComponentHighlighting

:thumbsup:
Updated submodule paths.