[REQUEST] Add .json extension to cached files

[Falki-git]

Benefit: less hassle/clicks when opening files, quicker. Faster iteration when developing patches.

Use case: edit patch, launch the game, PM caches the files, you quickly want to check what PM did. You open the zip file without unzipping and double click on a file without extracting it. If the file has an extension, it will automatically open with the default editor. If it doesn't, you get a popup where you have to scroll down to find the application you want to open with (WinRAR behavior).

[cheese3660]

@jan-bures I am assigning you for this, as the caching side of things is your work