Minor QoL update.

List of changes:

1. Updated nervous system manual - it now includes illustrations that show what the neural circuits are supposed to look like at each step;

2. Nervous system manuals now can be fully completed;

3. Propeller atoms are now optimized, don't reduce framerate. Also fixed a small bug that shortened their range in some cases;

4. Quality of life improvements to molecule editor. You can now see which atom you are targeting when setting parent atoms or individual connections between atoms. Also, molecule shapes now lock in even if you don't save;

5. Gonna be testing some options with the mainframe - shouldn't be too intrusive, and only for users that fully completed the tutorial.

   We also fixed some stability issues. Let us know if there is something we forgot or something you want fixed or improved, at it'll probably be in the next one!