Update sampleapps/messenger-platform to use opent2t library

[tjaffri]

Currently the sampleapps/messenger-platform/ sample does some ugly code here to find a translator by hard coded path then call methods directly on it.

Instead, we need to use the opent2t library and do this correctly, similar to how the cloud sample does it here.

We also should not have to download the entire git repo as we do in git.js and towards the end of app.js. All that should be cleaned up to use the official methods in the opent2t library.