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.
Correct error message.
Remove some levels of indentation.
Add "binary" format case. (not implemented.)
Exit if DataArray "format" is not known.
Add checks of other zlib error return codes.
Remove getXmlAttribute() and findDataArray from class interface.

This functions have nothing in common with BoostVtuInterface.
Move up readDataArray() for reading CellData/MaterialIDs.

Other DataArray will follow.
Use readDataArray() for reading Points.