Make space in CSS Grid tree for rule text

[seachel]

Node content for B overlaps the text for the inference from A. This may cause problems later when we wish to select a node.

Right now an inference is made of four rows, with the text of the inference centred over the middle two. To solve this problem, a single inference will have six rows:

1. rule text above
2. node content above divider
3. rule text for this inference
4. rule text for this inference
5. node content below divider
6. rule text below