Add LockedNext option to StoryItem

[birbilis]

StoryItem should have a "Lock" toggle button in its settings pane.
That should be off by default for new activities.
For older saved files that have tagged children should check if it can be set automatically

When the LockedNext is turned on, linear navigation using app's UI buttons shouldn't progress to Next (clicking on it should show lock button [as popup and maybe also on the Next button too / changing the button icon when drill is solved if any] as it does currently when moveable and non-moveable items with same tag are unmatched)

When is is turned off it should always progress to Next StoryPoint (even when there are unmatched tags [user should see some feedback popup btw [say an opening lock Lottie animation] when they match all tags and/or some animation of opening lock on the Next button if it's visible])

Useful to have this on state irrespective of tag-based-drill when one makes a StoryPoint that contains choice based navigation (either to external Story files or when having branching to other story points)