issue_show: Handle multi-line system notes better
issue_show: Handle multi-line system notes better

Right now, the date looks just slapped on at the end:

 * haeckse added 2 new commits

 * aafcd447 - foo bar
 * b04a23b7 - baz quz

 [Compare with previous version](/fancy-project/-/merge_requests/1234/diffs?diff_id=104473&start_sha=56c9cf766f56ece553c0b0da5deca859c8136bfc) at 2020-12-22 12:12:12

Instead, do the same as gitlab's web UI and handle the first line separately,
followed by the rest:

 * haeckse added 2 new commits at 2020-12-22 12:12:12

 * aafcd447 - [...]

zaquestion/lab,zaquestion/lab