Enhancement: Option to refresh when the application gains focus #201

I'm proposing a feature which could mitigate the issues that affect some of the users of the "Watch for changes in the repository" feature, me included. I suggest adding an alternative option to that feature which would refresh the view only when the application is brought to the foreground instead of whenever a change happens.

For reference, these are the issues I have experienced which led me to disable the "Watch for changes in the repository" feature. I've linked the relevant GitHub issues for the ones I found:

• Currently selected commit is lost.
• Context menu is closed on refresh.
• Commit list flashes: Reduce commit list flashing #131
• Git index is briefly locked: GitX locks repository for read-only access #164

I think all of those issues would be mitigated either completely or to some extent by such a new feature. Here is a more detailed description of how I would imagine that feature to work:

When that option is enabled, repositories are never continuously monitored for changes. Instead, whenever the application is brought to the foreground, the state of the repository of each open view is checked for changes once. If a change is detected, the view is refreshed. This kind of behavior is also in line with many document-based apps on macOS. When e.g. an image is opened with Preview and then changed using another application, the old image stays in Preview until it is brought to the foreground. This happens on an application-basis and not a document-basis. Or my IDE will reload the source files and refresh VCS states whenever it is brought to the foreground.

I'd be interested in hearing what you think!