Support Git LFS

[amit1rrr]

Typical git repository size increases in proportion to length of it's history. With edits to larger notebooks (say >10MB) the repo size could quickly grow to an uncomfortable level. Some users might even want to commit data files into the repository making the matter worse. This results in slow operations for git clone, git pull etc. Users would like to use Git LFS in these scenarios so it'd be great if we can support Git LFS in ReviewNB.

For completeness, there are few other ways to reduce repo size but they may not be ideal -

1. Run garbage collection git gc --aggressive --prune=now. This does not always work (especially if you've had lots of edits to large files).
2. Run bfg or git-filter-branch to delete large objects. This requires overwriting git history.

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Feel free to upvote/downvote the issue indicating whether you think this is useful feature or not. I also welcome additional questions/comments/discussion on the issue.