Improve commits page performance by loading commit details async

Problem to Solve

The /-/commits/master?ref_type=heads page currently loads all of the commit details when building the list. In projects which have long commit messages that require extensive markdown processing for links/users/etc... this request can be very slow.

Proposal

We should load the expanded body of the commit in an async request if the button to see it is clicked. This way we don't need to fetch the details for each commit message and process data which may never be shown.

Additional Details