Implemented the EVP skeleton class. Issue #22

[felix-zailskas]

Implemented a skeleton class for the EVP. This includes the following:

• The EstimatedValuePredictor class. This class now uses just LinearRegression to predict from dummy values. The function estimate_value can be used to get the value of a lead given its ID.
• The database package is a placeholder for the database we will use in the end. For now, it includes a singleton instance of a DatabaseDummy object. This object uses the dummy_leads.json file as its data. The dummies in that file are in accordance to the data field definition.
• The database package also contains the models.py and parsers.py files. Here models.py contains models that we might retrieve or store in the database. The Lead class is especially important here. I used the pydantic library for automatic field validation.

[luccalb]

Looks good, maybe you could add a tests/test_evp.py file that checks the evp outputs and will run during testing stage.

[felix-zailskas]

Looks good, maybe you could add a tests/test_evp.py file that checks the evp outputs and will run during testing stage.

Adjusted.

[luccalb]

Looks good!