This might seem controversial; in many cases the client code gets longer,
because it needs an extra line for an explicit `return nil`. I still prefer
this, because it makes it clearer which calls can return errors.
The comments that I'm deleting here explain why we need the bool; however, in
our case that's a theoretical issue. It would only arise if we ever were to pass
a nil context to SetParentContext, which we never do.
This is the highest priority of the escape actions because it's the thing you're
most likely to want to do upon hitting escape if you have a range selected.
Applying this to the staging/patch-building views is tricky: if we want this logic
for when a range of lines is selected, we'll also need to apply it when a hunk
is selected too. I still think it's worth it though: I've often accidentally
escaped from the staging view when trying to cancel a range selection.
We now always re-use the state of the repo if we're returning to it, and we always reset the windows to their default tabs.
We reset to default tabs because it's easy to implement. If people want to:
* have tab states be retained when switching
* have tab states specific to the current repo retained when switching back
Then we'll need to revisit this
