Tempo range improvements

[bryanbraun]

• Increase the tempo range. Maybe the max can be 180 or 200?
• The current slider is technically still hackable by changing the html range values in browser devtools. Should I try to prevent that?
  • It would probably be pretty easy by running all values through Math.max() and Math.min() right before setting to state.
• Update the styling to better match the color scheme and look consistent across browsers.
  • I like the display in Firefox the most... I'd be pretty happy if we got all browsers to look pretty close to that.
  • The number field shouldn't need changes.

[bryanbraun]

We almost went in this direction:

...but it felt like it drew too much attention, so we ended up doing this:

It was merged in 1ebc64d. Closing this now.