trivial cleanup

See merge request !195

Use one and the same ProcessedSample in all simulation threads

See merge request !194

Make all of Sample thread safe

See merge request !193

Make several classes in Sample thread safe

See merge request !192

To make them thread-safe.

This makes computations somewhat slower,
on my 4-core machine the test suite needs 105.8 s instead of 99.0 s.

merge ITerm -> ICompute

See merge request !190

Reorg dirs: move widgets from GUI/Views/IntensityDataWidgets to new directory GUI/Views/ProjectionWidgets

See merge request !191

Reorg dirs: move widgets from GUI/Views/JobWidgets to GUI/Views/FitWidgets

See merge request !189