Custom refspace dimensions

We currently hardcode the respace to be (in microns). I guess because it is the canonical setup.

```python
refspace = (
("coronal", (0, 13200),
("transverse", (0, 8000),
("sagittal", (0, 11400),
)
```
The problem is that sometimes parts of images are cut off after synchronization. The cleanest solution is to just allow for dynamic resizing of the refspace. Something like.

```python
refspace = (
("coronal", (c_max, c_min),
("transverse", (t_min, t_max),
("sagittal", (s_min, s_max),
)
```