Adding proper link to Sanbox / Environment, adding 3d secure support

Hi,

Just want to update this plugin:
- bumping the version to 1.3.0
- adding 3d secure support for Veritrans 2.0
- adding proper link to obtain client / server key for sandbox / production
- adding CHANGELOG file
- the veritrans library is now a subtree pointing to the veritrans-php remote repo

cheers,
uqi