Renaming from interface to calculator

[andped10]

A step towards a more readable code is made by renaming the handle to a third party calculator from interface -> calculator. As a part of this code change a wrapper class is introduced. The purpose of this wrapper class is to contain ALL code that enable our code to exchange data with the third party calculator.

calculators
   <name>
       calculator
       wrapper

Pull request implementing the changes #86

[andped10]

Pull request implementing the changes #86