Updates the plugin manager window to use the new failed module info.
Plugins installed in legacy folder locations are marked as Legacy with
a notice that will stop working in the future.
Plugins that failed to load are listed under an Errors section.
Plugins in the modules.json file that are not found are listed under
a Missing section. These entries can be removed from the modules.json
via a delete button.
This also cleans up some other small issues and updates the dialog
buttons to be Save/Discard instead of Ok/Close.
Warchamp7
5c32e2f408