[BUG] custom Grid.__repr__ logic is lost when extending a Grid

[Thijss]

Probably due to @DataClass decorator..

[vincentkoppen]

We discussed that it currently isn't possible to provide a clean solution.
Suggested solution:

• Provide the current implementation as _repr and change __repr__ to:

def __repr__(self): 
   self._repr()

• Users can now add the same code to their own grid extension
  • Add a test in our codebase to test that this works correctly.

[vincentkoppen]

Long term we want to remove the @dataclass from the Grid, but this is breaking so can only be done in a 2.0 version