Fixed a large re-structuring to use snowplow-tracker-core

- Fixes #66
Removing Version from gitignore temporarily
Removed .core package
Revert "Removed .core package"

This reverts commit 21fd296818a84e6d38d6d5caab8b0767e673cb31.
Initial bit to fix the Versioning problem

- Extending the classes
Added Tracker, Subject & Emitter classes with super
Add original map instead of mapString
Fixed failing test
Added TransactionItem in tracker package
Added comments into the extended classes
Moved TransactionItem to correct package
Added copyright to top of class
Merge pull request #67 from snowplow/develop

Version 0.5.0 with Version class fix