Diffs is getting messy let's remove the comment toggle button.

In trying to keep the diff area clean the title could be cleaned up if we remove the toggle comments buttons. It would be great if we could keep it down to 1 button but two max.

cc @dzaporozhets

Collapse/Expand diff comments

Here is a quick prototype of the interaction with the profile avatars on diff comments:

Diff view options dropdown

I've also made a mockup of the dropdown that combines the diff view options. This allows for the jump to next conversation to be next to the other discussion options as discussion here: https://gitlab.com/gitlab-org/gitlab-ce/issues/10325#note_13442912