Refactoring WrapperR structure

[manuparra]

Add new level before with the name: /wrappers/

And this is the structure:

/wrappers/
Contains: init.py
/wrappers/wrapperR/
Contains: dataset.py, ...., wrapperv2.py
`/wrappers/wrapperR/methods/
Contains: methods from wrapperv2.py in a file --> lm.py, cor.py, lr.py rf.py arima.py.

[Mancuerna]

Done.