Add spinner for long running operations

[protoEvangelion]

When switching to a branch that has a lot of changes compared to the current branch, it would be nice to see some sort of UI indicator that lets me know that the check-it-out process is not frozen. There is a good one in this library: https://github.com/oclif/cli-ux

[jwu910]

The blessed widget https://github.com/chjj/blessed/blob/master/lib/widgets/loading.js loading has something like this built in to the dependency Maybe a good idea to take a look to see if we can this can be implemented

[protoEvangelion]

https://www.npmjs.com/package/blessed#loading-from-box

[jwu910]

@protoEvangelion Yup! Same one, it's currently being used on the refresh command.

[jwu910]

Should fix #246