Add autoclose option.

[zbindenren]

Is your feature request related to a problem? Please describe.
I often stage, commit and then push changes. Then I have to close the the neogit view.

Describe the solution you'd like
Would be cool that after push is finished and succeded, neogit closes automatically.

Or we could have something like:

autoclose_on: commit|push|pull

Describe alternatives you've considered
Close manually :-)

Additional context
I know this is only for lazy people like me.

[gegoune]

Or maybe introduce events which users could subscribe to, would cover that case and, I assume, many others without being too specific about implementation on neogit side.

[TimUntersberger]

I'd say just using vim user autocommands like we did for the refresh event should be fine.