Feature/import old database data to equal package

[lucaslaurent04]

Allows to import data from an old database to the eQual database by mapping fields using a json configuration file:

Example of init/import-config.json for a package named bakery:

[
    {
        "entity": "bakery\\Bread",
        "old_table": {
            "table": "breads",
            "id_field": "id_bread",
            "fields": {
                "id_bread": "integer",
                "label": "string",
                "price": "float"
            }
        },
        "data_map": {
            "id": "id_bread",
            "name": "label",
            "price": "price"
        }
    }
]