Add ability to reload Plugins

[nikeee]

This is somehow weird. We don't want to add a FileSystemWatcher because as soon as every plugin is configured, it is purely overhead as it doesn't really change anymore.

The standard FileSystemWatcher uses a kernel hook while there is a PollingFileSystemWatcher that uses polling. Both seem too much.

Maybe a "reload plugins" button in the context menu or the plugin list wo suffice?

[nikeee]

Also, a button to remove/delete plugins would be cool. Deleting if DLL plugins while running would be hard, I guess.