Add path placeholders for threads

[CanePlayz]

Closes #1123

This pull request introduces three new path parameters (currently called %x, %y, and %z because that was what came to my mind, please let me know of alternatives that make more sense). If the exported channel is a thread, these parameters are resolved to either the ID, the position, or the name of the thread's parent channel.

If the channel isn't a thread, the entire structure where one of these parameters is included (//...%y...//) is removed. The PR also modifies the logic of the category placeholders so that these correctly resolve to the category if the exported channel is a thread and not to its parent channel.

Previously, it wasn't possible to include both the category and the parent channel in the path of an exported thread.

I've also added .vscode/ to the .gitignore file since I prefer working with VS Code, but feel free to remove it if it shouldn't be there for some reason.

Also, please let me know if there's a better way to do it and to improve my coding style, I have almost no experience with C#.

In case this approach will be accepted, I'll also add the documentation for it.

[CanePlayz]

On this topic, is there any pattern in the current naming scheme of path placeholders or in the way they are structured in the code (these blocks of two parameters)?