Dummy texture importer

Added a dummy importer for textures to use with the server platform.
Allows for running a project in headless mode without crashing when loading scenes containing textured objects
Also as a result decreases load time as no image files have to be loaded.

platform/server/os_server.cpp

@@ -30,6 +30,7 @@
 #include "os_server.h"
 #include "drivers/dummy/audio_driver_dummy.h"
 #include "drivers/dummy/rasterizer_dummy.h"
+#include "drivers/dummy/texture_loader_dummy.h"
 #include "print_string.h"
 #include "servers/visual/visual_server_raster.h"
 #include <stdio.h>
@@ -83,6 +84,9 @@ Error OS_Server::initialize(const VideoMode &p_desired, int p_video_driver, int
 
 	_ensure_user_data_dir();
 
+	resource_loader_dummy = memnew(ResourceFormatDummyTexture);
+	ResourceLoader::add_resource_format_loader(resource_loader_dummy);
+
 	return OK;
 }
 
@@ -99,6 +103,8 @@ void OS_Server::finalize() {
 
 	memdelete(power_manager);
 
+	memdelete(resource_loader_dummy);
+
 	args.clear();
 }