`git smartlog` should render only revset commits

[arxanas]

As discussed in #474. Currently, git smartlog shows all commits in the provided revset as well as all commits which are pointed to by a branch or HEAD, and their ancestors up to the main branch. Ideally, we would not show commits with branches unless specified, and we would abbreviate any ranges which are necessary to show the topology with the main branch but weren't explicitly specified.

[arxanas]

This was implemented by @claytonrcarter in #619 😊.