Because they are stored twice: Once in the CFG of the script, and once in the CFG of the machine instance.
Fixes an issue reported here: https://github.com/Ultimaker/Cura/pull/3229
The problem was that Python's ConfigParser doesn't preserve case. Everything becomes lowercase. Some post-processing scripts have uppercase characters in their setting keys and these weren't preserved.
This fix configures the ConfigParser to pass the setting keys untransformed. The transformation function becomes the str() function which just passes the input through untransformed.
On Windows and OSX, resources and preferences are stored in the same folder. On Linux, preferences are in ~/.config, resources are in ~/.local/shared. Postprocessing scripts belong in the latter, along with all the other resources (definitions, plugins, themes).
Fixes#3356
This is more efficient, because we're not writing every time you modify the list of scripts. It's also more complete, since if you don't modify the list of scripts but just modify one of the settings, that setting change also gets written to the stack after closing the window.
So that you're not getting into a state of viewing an invalid index. If you switch to a printer with 0 scripts attached, the index is still invalid, but it won't display anything then so you're okay.
This causes the button to display immediately on start-up if there were any post-processing scripts in the current machine. If there weren't, then no button will be shown (as specified in the QML).
Previously the QML was only loaded first upon clicking the item in the extensions menu. Now it has to be loaded on start-up in order to display that button.
