Increase lines of context in the diff view by increments; don't jump straight to the full file

[philc]

I watched both Sean and Nimrod use this feature the other day. They both wanted to see more context, and I showed them the hidden keyboard shortcut for it (we should add a non-keybroad driven UI for context as well). When they hit the shortcut to show the entire file, thousands of lines suddenly appeared and it was then hard to navigate between the diff chunks.

We should instead add a UI and shortcuts to increase or decrease the context by hunks of 10 lines or so.

[bkad]

i'll tackle this after my bugs in progress

[bkad]

fixed in 6ae7308

[philc]

epic