Updated GitIgnore and Plugin Path Resolution, plus dependancy resolution

[AlienXAXS]

Hi Warp :)

This PR resolves a few things:

1. Adds a Visual Studio C# Gitignore file that will no longer want to upload debug/temp/etc files to your repo
2. Fixes the Manifest file path lookup. This means you no longer need to statically define your plugin folder path within your codebase.
3. Removes envrionment.props from each project and moves it to a global Directory.Build.Props file (.example file isnt gitignored) that all underlying projects use for Valheim paths.
4. Uses BepInEx's publicizer against the DLL's already found within the Managed\Valheim_Data folder.
5. Moves shared libs to the GlobalLibs folder within the projects root directory to reduce clutter.