ecere,ecereCOM: support Emscriptem platform. add new Emscripten interface driver.
 - <NOTE> had to move GetDisplayDriver and GetDisplaySystem to end of Display.ec file due to compiler issue
 - #if !defined(__EMSCRIPTEN__) out:
    - dynamic loading
    - thread/mutex/semaphore and Condition class
    - file monitoring
    - png/jpeg/gif
    - X driver
    - NCurses driver
    - dcom
 - add emscripten_main_loop_callback in GuiApplication.ec
 - use of glfw and a bit of tweaking in the OpenGL driver