Avoid presenting errors from a detached view controller.

Doesn't seem to actually be an issue, but I wanted to avoid logging.
Flash scroll indicators when in-app action sheet appears.

This may or may not be sufficient to show that there are more actions than currently visible, but it's something we should be doing regardless.
KVO WKWebView's -loading property for the app's network indicator.

WKNavigationDelegate isn't the answer for this.