Stats: Add a slider bar to sparkline.

Added a slider bar to sparkline, which shows how many views were there during that hour.
Stat: Refactor sparkline js.

- Reuse drawing logic for drawing all bars in the beginning
- Better naming
Stats: Style views label.

Style the views label in sparkline.
Stats: Hide views label on mouseout.

Don't show the sparkline views label when moving out of the canvas.
Stats: Update sparkline colors.

Change the stats selector color.
Stats: Fix sparkline hover height.

Sparkline menu item now as high as the admin bar.