R1:0f9f8b5f3058

Tidy context displayed in gap

Summary:
We have some complaints on this feature:

- It's not clear that the displayed code is context from gap.
- It would be better if the context would be displayed with its real indentation.
- It's not clear how far the context is from the displayed code.
- Links revealing gap aren't on consistent place.

This solves all these problems and introduces new one:
It now seems that the reveal links works only with the left side.
Anyway, I think that this is better overall.

I…