Resolve ""Merge when pipeline succeeds" visible if approvals are pending"

This MR fixes a regression introduced here (https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/1091) that inadvertantly removed DOM listeners in the accept template responsible for disabling the primary merge acceptance button.

It also disables a few more variations of merge acceptance buttons when approval has not been fully given, including the rebase button.

Closes #1595 (closed)