WIP: temporarily highlight the "read all" navbar button when clicked.

This gives the user a visual indicator of the action he's requested.
Improved highlight animation when clicking on the "read all" navbar button.
Changed easing function for highlight animation when clicking of "read all" navbar button.

Now it stays longer in the "highlighted" state, without changing total animation duration.
Break down navbar fragment into several smaller fragments.

The ERB fragment for the navbar had become too complex. Better to breat it down into sub-fragments.
Temporarily highlight the show/hide read button in the navbar when clicked.
Correct a 1px error in navbar height.