move stb_image/stb_image_write.cpp into a cpp file instead of random files with the magic 'STB_IMAGE_WRITE_IMPLEMENTATION' define

move setup.py back to eglRenderer extension, use pkgutil.get_loader('eglRenderer').get_filename()
disable dlmopen by default, unless B3_USE_DLMOPEN is defined.

test/GwenOpenGLTest/premake4.lua

@@ -41,6 +41,7 @@
  		"../../examples/OpenGLWindow/opengl_fontstashcallbacks.h",
 		"../../examples/Utils/b3Clock.cpp",
 		"../../examples/Utils/b3Clock.h",
+		"../../examples/ThirdPartyLibs/stb_image/stb_image_write.cpp",
 		"**.cpp",
 		"**.h",
 	}