Search all subdirectories for Plugins

This was added in #801 which broke the previous plugin install
behaviour. Previously plugins could be loaded from subdirectories
but this search was only for the highest level. Change it to search
all subdirectories instead to restore the previous behaviour.

Also modifies the same option from #934, though I'm not 100% sure
if this is needed here.

Emby.Server.Implementations/ApplicationHost.cs

@@ -1047,7 +1047,7 @@ namespace Emby.Server.Implementations
         private async void PluginInstalled(object sender, GenericEventArgs<PackageVersionInfo> args)
         {
             string dir = Path.Combine(ApplicationPaths.PluginsPath, Path.GetFileNameWithoutExtension(args.Argument.targetFilename));
-            var types = Directory.EnumerateFiles(dir, "*.dll", SearchOption.TopDirectoryOnly)
+            var types = Directory.EnumerateFiles(dir, "*.dll", SearchOption.AllDirectories)
                         .Select(x => Assembly.LoadFrom(x))
                         .SelectMany(x => x.ExportedTypes)
                         .Where(x => x.IsClass && !x.IsAbstract && !x.IsInterface && !x.IsGenericType)
@@ -1346,7 +1346,7 @@ namespace Emby.Server.Implementations
         {
             if (Directory.Exists(ApplicationPaths.PluginsPath))
             {
-                foreach (var file in Directory.EnumerateFiles(ApplicationPaths.PluginsPath, "*.dll", SearchOption.TopDirectoryOnly))
+                foreach (var file in Directory.EnumerateFiles(ApplicationPaths.PluginsPath, "*.dll", SearchOption.AllDirectories))
                 {
                     Logger.LogInformation("Loading assembly {Path}", file);
                     yield return Assembly.LoadFrom(file);