Make initialization parameters mandatory for Entity class

[G2Pavon]

Currently, the Entity class is initialized with Entity.__init__(self), which lacks specificity and might lead to incomplete entity initialization. Change the initialization to Entity.__init__(self, classname, origin_or_brushes, properties=None)
classname is fundamental for entities, and making it a requirement in the initialization helps ensure that entities are properly identified.
For point entities, origin is fundamental, while for brush entities brushes are. These parameters should be explicitly required during initialization to avoid incomplete entity states

[G2Pavon]

now they are optional but not required: 59fc5cb

• TODO: make them required (Requirements: Refactor load_map())