uggrid: get rid of `UGMakeableEntity`
Just use Entity
directly instead and access the setToTarget()
method via entity.impl().setToTarget()
.
With this chage the user-provided gather
and scatter
methods are
also called with instances of the Entity
facade class instead of a
derived class. This makes it easier to overload them for different
codimensions of entities (by overloading them for the different types
of Entity
).