Implement mod zip unpacking

[4onen]

As it says on the tin, implements unpacking of zip files that contain acceptably-formatted AwSW mods.

Purpose

To make non-Steam-Workshop mod installation easier.

Code process

After the mod folder list is compiled with reset_mods(), but before any mods are imported, this PR separates out and removes files whose lowercase path end in ".zip".

The implementation assumes the mod is implemented using an __init__.py at the root of the mod directory, as is the currently accepted mod format. It solves for zip files being nasty and nesting folders by finding the shallowest folder containing an __init__.py and extracting that + all siblings and siblings' descendants. If multiple folders have an __init__.py at the same depth, it errors out. If no __init__.py exists in the zip, it errors out.

The folder name for the extracted mod is the name of the zip without the ".zip" extension. If a folder already exists with that name, the m_time of the zip and folder are compared. If the zip is newer, the folder is recursively deleted and the zip file's contents are extracted into a fresh folder.

This process is performed for all zip files found in the mod directory. If any zip has been unpacked (after the m_time checks) then the game restarts entirely, exactly as if the user had clicked Remove mod and reload on an error screen.

Drawbacks

• Fully reloads the game if any zips get unpacked. Not bad per-se but means it takes a few more seconds to boot on mod update on underpowered platforms. Only adds minimal overhead (stat n zip files, stat n folders up to twice) on subsequent boots.