VERSION 0.115.1258: important tonemapping changes and other things

Finally I found the time to dive into the tonnemapping problems which existed for a while and which affected both final renders and the real-time-preview, but in different ways.

The tonemapping is much more stable now, especially in the previews, and overall produces very nice images.

Also, I have a added a browser for random-flame-generators, because the listbox had became so long, that it was unusable. This also gives the opportunity to provide brief descriptions and mark certain random generators as favorite.

And, it is now possible to move nodes up/down (using the the edit-menu). This applies to layers, xforms, final xforms and variations.

And, you can now see the code of all variations inside the variation-browser. This may be very helpful when you plan to create your own (custom) variations.

Complete changelog:
VERSION 0.115.1258 (20.08.2025):
- rendering: fixed a problem with the brightness calculation (SWAN-101)
- rendering: fixed a problem in the realtime-rendering which sometimes caused
the flame to render too bright (SWAN-97)
- main-editor: replaced the listbox for random-flame-generators by a
random-flame-generators-browser-window, because the list has become too long
now and scrolling does not work either (SWAN-133)
- random-flame-generators can now be marked as favorite now
- main-edtitor: select a random favorite random-flame-generator at
startup (if any)
- variation-browser/preview: the preview now also takes the variation-amount
into account (together with an view-scale-factor, which may be changd by
dragging the mouse). This is way more intuitive, because increasing the amount
also increases the size of the preview
- added a description panel to the random-flame-generators-browser-window
- new "julia_gasket"-variation
- added some random-flame-generator-descriptions
- flame-editor: added a function to move certain node up/down (via edit-menu) (SWAN-134):
- layers
- xforms
- final xforms
- variations
- flame-editor: removed the complete re-render of the preview after changing values
using a slider and releasing the slider, because the tonemapping-problem is now fixed
- variation-browser: show also the glsl-code of an variation (mainly for inspiration)
- main-editor: added some shortcuts for loading/saving flames etc. (you see them
at the menu items)
- variation-browser: added code-reformatting for display of glsl-code
- variation-browser: also display variation-specific glsl-functions when
displaying glsl-code
- variation-browser: also display code of the inverse transform when showing glsl-code
of a pre_post-variation