Improve the layout and scaling of the user interface so that scrolling isn't necessary

[colinbdclark]

The MovementOSC user interface is pretty rough. Most video resolutions end up causing the UI to scroll—the video canvas should be scaled to suit the window size. Below the canvas is a video element set to hidden, which means it still takes up space on the page.

If I remember correctly, both Bubbles and Aconite have a means to properly hide the video element, so it's worth looking at their stylesheets.