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* this is achieved by avoiding allocating a chunk of memory for the image on the
  GPU each time, but rather reusing the same buffer over and over.
* Added some comments to the solver code

attenuations were not computed correctly

On my machine this means a performance increase from 8ms to <1ms. Time that can
be spent running more iterations of the CG algorithm to get more accurate solutions.

Switch wrapping mode for texture in fan renderer, so that colors don't
bleed to the other sides on the edges.

Now the pipeline correctly uses the fused confidence image as input
for the fan geometry rendering.

The texture has the same size as the original us-image

warnings were caused by incorrect signature of updateProperties method

* Added GlImageResampler processor to lower the resolution of the US image
* Exposed solver parameters to the GUI
* Added AdvancedUSVisualization processor to display the data

This visualization overlays a solid color to the image, with the opacity
determined by the uncertainty.

* Fixed out-of bounds warnings, when showing 2D-Textures in Inspector
* Fixed bug introduced in 719004e0 which would crash the application when the
  PipelineTreeWidget had no item selected (e.g. when adding a new Pipeline)

Code still needs to be cleaned up a lot, and settings need to be exposed
to the GUI.

Now it is possible to change the property window just by navigating
the PipelineTreeWidget with the arrow keys

in the property window.
As this causes the property widget to move each time the user clicks on a
processor.

Procfactory

See merge request !110