Simplify analytics handling, refs item:283

Instead of annotating each view, we can leverage UI Router's [state change
events](https://github.com/angular-ui/ui-router/wiki#state-change-events) to track which views are viewed.

Attaching a directive to each view is costly and increases maintenance burden.

Rename click tracker to `gaClick` (Google Analytics click) for clarity and for familiarity with other Angular directives (e.g. `ngClick`).