Move timeline slider out of status bar

[JasonWeill]

Problem

I read @Meriem-BenIsmail's blog post about the document timeline slider — congratulations on the launch! I was talking about this with a teammate who suggested moving the timeline slider out of the status bar. The status bar is primarily intended to convey status information, and especially on smaller screens, it is limited in width.

Proposed Solution

Retain the document timeline slider, but in the status bar, display only a "history" button that causes the slider to appear in a separate control, above the status bar. For reference, Windows 10's volume slider works like this: clicking on an audio button causes a slider to appear so that people can change the volume.

This will allow for more UI elements to be displayed in the slider, such as annotations for times or checkpoints, and will free up horizontal space in the status bar.

[krassowski]

In review of related PR I also suggested moving it to sidebar. It could then show reference points like time or hour associated withe the document state at specific intervals.