Add visual indicator when a fatal failure occurs

When a fatal failure occurs, a error indicator is added to the status bar, flashes red once, and then turns back to transparent background.

A modal dialog will open when the indicator is clicked, reporting the error, and providing a way to go to the error in the document.

The status bar indicator will go away as soon as Reporter.prototype.checkFatal returns false (no more fatal error).

The formatting and text can probably be worked on, but this is my initial commit for this subject.
Ideally, I wouldn't have to specify `INDICATOR_CLASSES` or `INDICATOR_TOOLTIP` here, as that overwrites any post-applied classes (and/or tooltip changes). Perhaps we could query `$statusBarIndicator` for the current classes & tooltip.