Add pan/zoom reset button

[subdavis]

• Remove explicit column sizes in control bar.
• add button with tooltip to reset zoom/pan of video, mostly helpful while annotating a polygon.

Wait for upstream to merge, blocked on #270

[subdavis]

Realized I needed to add the option to the help menu, and I figured it'd be a good idea to style it as "flat" to match the rest of the app. While I was there, I fixed a bit of alignment.

Before

After

[subdavis]

Fixed. Added index to key, added some min-width. Since app injects arbitrary-width controls into those slots, I made controls only aware of the play/skip width and constrained the window width to at least 700. Anything below 1200 is unusable to me, but we really shouldn't be attempting to support mobile-width layouts IMO.

[BryonLewis]

Looks good, I also agree with the not supporting mobile. My intent wasn't to support mobile, just not get weird when making the window small, who knows why but given a public facing user base someone will try to utilize it in a narrow window.