Fixed error ParameterSpace.columns()

**Problem:**
Setting attributes of shape `(n, 1)` fails for Projections.

**Reason:**
`lazyarray.partial_shape(...)` in `ParameterSpace.evaluate(...)` strips dimensions containing only as single element. However, this information is important for the `.columns()` and `.__iter__()` functions to distinguish cases where there is a single row from a single column. 

**Solution:**
The most straightforward solution was to copy `partial_shape(...)` from lazyarray but to omit the dimension-reduction step. As the `.__iter__()` and `.columns()` functions are the only ones accessing the `_evaluated_shape` attribute.