CB-6322 Simplify platforms/platform code for platform specifics

github: close #146
CB-6292 Revert commits that add explicit callbacks to APIs

The APIs already have callback-based APIs when called through the
`cordova` module (code is fairly confusing, but is in
addModuleProperty)
CB-6292 Add a callback-based API for cordova info (in addition to promise API)

Also adds a comment explaining how to use the callback vs. promise API.
CB-6292 Actually add a comment (meant to be a part of prev. commit)