I just implemented a small UI improvement: there is now an option that allows to place the histogram and layer list on the right of the preview:
A restart of the application is needed for the new setting to take effect…
Next step will be add an option to put the active tool controls into a floating dialog (instead of the bottom of the layers list as it is right now). This should give more space for the layers list itself, and allow to place the controls anywhere on the screen. What do you think?