Implement global objects as functions that return a single instance

[loathingKernel]

As the title suggests, remove the global objects in shared and instead used functions to instantiate or return them.

They are still reside in rare.shared but that doesn't need to be the case any more. They can be moved into the same files
where each class is implemented for better concept encapsulation. I left them there to make the change-set as minimal as possible
because we have various branches running around right now.

I also sneaked in a few worker signal classes renames, as it was getting confusing to keep track what signals each field was referring too.

[Dummerle]

Does it work now for HiDPI devices?

[loathingKernel]

No, that HiDPI commit is just for the qtawesome icons to scale properly. MultisampledNight asked if I could add it to the PR on discord.