Add IAC support for HTML5 (DEF-1782)

[AGulev]

It would be nice if it was possible to pass in arguments to an HTML5 app and pick them up in the Lua code using same IAC module as we have on Android and iOS.

For now we can work around the problem of passing in a session token and core user id on canvas like this (thanks [~sven.andersson]):

Module.runMain(configure=html5.external_generated_token=abc123)

sys.get_config("html5.external_generated_token)

Case: for the current config usage this is a potential security risk