Changes from comment set #1

Corrected files: MessageType.as, NDTConstants.as, NDTUtils.as, Main.as
Fix previous commit mistake
Additions from JS Callbacks Document

All changes done except SWF Parameters Hostname TestSuite
Changes from comments set#1
Changes from comments set#2

1. Removed unnecessary import
2. Added HTML tag constants to NDTConstants
3. Restructured function initializeFromHTML
Merge pull request #4 from anantsubramanian/js-callbacks

Js callbacks