Refactor | Moving common functions out

* Moving batch convert to milis to commons

* Updating all references
Adding more tests, refactoring code

* Adding tests to cover more of the VariableTimeseriesEngine.
* Making all private functions also start with an underscore for
  readability
* Accepting generics instead of specifics (List and not ArrayList)
Adding test cases

* Modify points tested
* Adding one more for add points