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.h

@@ -32,6 +32,7 @@
 
 #include "../x11/crash_handler_x11.h"
 #include "../x11/power_x11.h"
+#include "drivers/dummy/texture_loader_dummy.h"
 #include "drivers/rtaudio/audio_driver_rtaudio.h"
 #include "drivers/unix/os_unix.h"
 #include "main/input_default.h"
@@ -65,6 +66,8 @@ class OS_Server : public OS_Unix {
 
 	CrashHandler crash_handler;
 
+	ResourceFormatDummyTexture *resource_loader_dummy;
+
 protected:
 	virtual int get_video_driver_count() const;
 	virtual const char *get_video_driver_name(int p_driver) const;