Implemented stack creation and did some optimisations.

ExtendedStackToImage is a modified version of StackToImage. The extended
version gives the opportunity to sort the images.

A GenericDialog is used to select the mode of drift detection. A
YesNoCancelDialog was used until now.
Added a message that informs about the not yet implemented manual mode.
OptimisedStackShifter uses the right title if a new image is created.
Implemented the parameter dialog for StackShifterPlugin.

I added 2 numeric fields for each slice of the selected stack. The user
can choose to applay the entered shift, or he can use the automatic
optimisation.
Started to implement the ElementalMappingPlugin.

The main part of the parameter dialog is finished. I recycled the code
of my old elemental mapping plugin to read out the energy loss by using
regular expressions (EnergyLossExtractor) and to identify the ionisation
edge.