Ryven

Added:
- **source code preview!** You can now see the source code of a placed node inside the editor. A basic syntax highlighting works too. I will add the option to also show any node's widget classes in the future.
- NodeInstance and OutputPin highlighting on mouse hover
- direct data output value access on mouse hover (over the gate/pin)

Reimplemented:
- the whole selection procedure, now using the built-in system by `QGraphicsScene` and a std `RubberBandSelection`
- undo/redo system which now does not rely on indices anymore but instead holds references to the actual objects. A removed object does not get recreated when undoing the remove anymore but the actual object just gets placed in the scene again which is pretty nice. (same for all flow commands)
- Log enabling/disabling process, now working fine with the new undo/redo system

And many small internal adjustments. The only big change left is the reimplementation of the geometric organization of a NodeInstance's contents via `QGraphicsWidgets` and `QGraphicsLayouts`. This will make the code much cleaner but isn't of the essence for the user.

I removed tokens. This enables slightly easier and more open programming of nodes. Along with that, I changed the algorithm executing the script, so that now data connections are always forward updated on change and not backward updated on request. This makes execution flows slower but pure data flows faster and simpler. I would like to create some live video and audio processing nodes in this version to show what it is capable of. The biggest issue is currently performance when combining dataflows with execution nodes.

First pre-release of this software! This is the prototype that can be seen in a demo YouTube video. It includes basic functionality including a system for dynamically creating and importing nodes and a mostly working flow execution algorithm.

The next releases will be about improving the NodeManager and adding new content. The documentation will experience a lot of improvement too, I think.