Animated navbar dropdowns with Velocity.js in the read view.

Not yet implemented:
- animation of the user dropdown in edit profile view
- animation of social sharing dropdown
- animation of locale dropdown
Make dropdown menus fill the containing element's width.

This does not change the app aspect in desktops, but in mobile the close animation looks better.
Animate with Velocity.js the opening/closing of the entries social sharing menu.
Enable user dropdown animation in edit profile view.
Animate the locale swicher menu opening and closing, using Velocity.js.