feat(topbar): New topbar component.

`&` produces in a function that is executed in the context of the parent scope, whereas `=` sets up bi-directional binding between the isolate scope and parent scope.  In this case I believe `=` is what you want, since we just want to data-bind the `isHover` attribute between the parent scope and isolate scope, and don't need it to be a function that executes in the context of the parent scope. Additionally because `scope.isHover` is a function, the code as written doesn't work as intended, as `scope.isHover` will always be truthy.