- the purpose of this constructor method is to generate all `Pixel`s
for a `Grid` that have at least one `Address` assigned to them
- fix missing `UniqueConstraint` in `Grid` class => it was not possible
to create two `Grid`s with the same `.side_length` in different cities
- change the `City.viewport` property into two separate `City.southwest`
and `City.northeast` properties; also add `City.total_x` and
`City.total_y` properties for convenience
- the old `UTMCoordinate` class becomes the new `Location` class
- its main purpose is to represent locations in both lat-long
coordinates as well as in the UTM system
- remove `Address.__init__()` and `City.__init__()` methods as they
are not executed for entries retrieved from the database
- simplfiy the `Location.__init__()` => remove `relative_to` argument
- the Address.x and Address.y properties use the UTMCoordinate class
behind the scenes
- x and y are simple coordinates in an x-y plane
- the (0, 0) origin is the southwest corner of Address.city.viewport
- create `*Factory` classes with fakerboy and faker that generate
randomized instances of the ORM models
- add new pytest marker: "db" are the integration tests involving the
database whereas "e2e" will be all other integration tests
- streamline the docstrings in the ORM models
- use SQLAlchemy (and PostgreSQL) to model the ORM layer
- add the following models:
+ Address => modelling all kinds of addresses
+ City => model the three target cities
+ Courier => model the UDP's couriers
+ Customer => model the UDP's customers
+ Order => model the orders received by the UDP
+ Restaurant => model the restaurants active on the UDP
- so far, the emphasis lies on expression the Foreign Key
and Check Constraints that are used to validate the assumptions
inherent to the cleanded data
- provide database-independent unit tests with 100% coverage
- provide additional integration tests ("e2e") that commit data to
a PostgreSQL instance to validate that the constraints work
- adapt linting rules a bit
