Refactor Contents tab refreshing

[HebaruSan]

Problem

The Contents tab refreshes and shows the mod contents if you download a mod via the Download button or right click menu, but not if it is downloaded during installation.

Cause

Refreshing cache-related state (including the Contents tab) is handled (duplicatively) at the places where GUI stores or purges a mod, but when you install an uncached mod, it is downloaded and stored by ModuleInstaller, so GUI doesn't react.

This is a brittle approach because it has a many-to-many structure, where each place that deals with the cache must also handle all of the secondary consequences itself.

Changes

• Now NetModuleCache has ModStored and ModPurged events that it fires whenever mods are stored or purged, including during mod installation. If all mods are purged, ModPurged's module parameter will be null.
• The logic for reacting to cache changes is consolidated into one GUI.Main.OnModStoredOrPurged function, which is used to handle the new events, including during installation. Places that formerly triggered the refresh now no longer do, because they don't need to anymore.
• UpdateCachedByDownloads can now handle updating the full mod list's IsCached property when its parameter is null, for when the user clears the cache in the settings
• ManageMods.OnSelectedModuleChanged now no longer sets ModInfo's active mod when the Manage Mods tab is not active, for when OnModStoredOrPurged refilters the mod list in the background during installs, because this causes ModInfo to become visible when it shouldn't. It will still be set when the Manage Mods tab becomes active again.

Fixes #3998.