refactor: invert the last engine-to-UI dependencies

- NodeFactory's menu creation moves to UI-side widget/menu/factorymenu
  (the factory only exposes its node library read-only now)
- DiskManager's cache-settings dialog is created through a registered
  std::function handler (registered by Core at startup)
- OlivePluginInstance creates progress UIs through a
  PluginProgressReporter interface (Null fallback headless) and queries
  the active viewer through a provider callback, both registered by Core
- factory.h, diskmanager and pluginSupport no longer reference any
  widget//dialog//panel//window headers or classes

app/render/diskmanager.cpp

@@ -31,13 +31,15 @@
 #include "common/filefunctions.h"
 #include "config/config.h"
 #include "coreengine.h"
-#include "dialog/diskcache/diskcachedialog.h"
 
 namespace olive
 {
 
 DiskManager *DiskManager::instance_ = nullptr;
 
+DiskManager::ShowDiskCacheSettingsHandler
+	DiskManager::show_disk_cache_settings_handler_;
+
 DiskManager::DiskManager()
 {
 	// Add default cache location
@@ -181,11 +183,21 @@ QString DiskManager::get_default_disk_cache_path()
 		.filePath("mediacache");
 }
 
+void DiskManager::set_show_disk_cache_settings_handler(
+	ShowDiskCacheSettingsHandler handler)
+{
+	show_disk_cache_settings_handler_ = std::move(handler);
+}
+
 void DiskManager::show_disk_cache_settings_dialog(DiskCacheFolder *folder,
 											  QWidget *parent)
 {
-	DiskCacheDialog d(folder, parent);
-	d.exec();
+	if (show_disk_cache_settings_handler_) {
+		show_disk_cache_settings_handler_(folder, parent);
+		return;
+	}
+
+	qWarning() << "No disk cache settings dialog handler registered, skipping";
 }
 
 void DiskManager::show_disk_cache_settings_dialog(const QString &path,