* fix commit view JS features, reimplement folding

File content folding was not working so I reimplemented it in a saner
way. Then I noticed the issue was actually because of missing JS
libraries (seen on the console of every commit with error
'SimpleMDE is not defined').

Fixed the libraries. I think the reimplementation is worth to keep.

* add .closest polyfill

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>