feat: basic plugin system

The wayland plugin now uses it.

src/core/main.cpp

@@ -8,6 +8,7 @@
 #include <qstandardpaths.h>
 #include <qstring.h>
 
+#include "plugin.hpp"
 #include "rootwrapper.hpp"
 
 int main(int argc, char** argv) {
@@ -38,6 +39,8 @@ int main(int argc, char** argv) {
 		return -1;
 	}
 
+	QuickshellPlugin::initPlugins();
+
 	// Base window transparency appears to be additive.
 	// Use a fully transparent window with a colored rect.
 	QQuickWindow::setDefaultAlphaBuffer(true);