Added a GenericDialog to SR-EELS_characterisation.ijm

The dialogue shows the automatically determined parameters and allows
the user to modify them.

I added *.ijm and *.plt to the gitattributes file, to enable automatic
line ending conversion.
JPEG-images use logarithmic scale.

Regions with low signals are better visible now. I had to change the
colour of the overlay points, because yellow and orange are barely
visible on bright background.