- Remove border styling from clip, transition objects
- Remove box-sizing: border-box, which made objects' DOM size unreliable
- Create new CSS class .tl-border, to hold border styling
- Insert new div.tl-border container just inside each clip/transition
- Remove sizing-bug "fudge factors" (like bounding_box_padding)
- Implement all highlight/hover styling in pure CSS (with `:hover`),
  eliminating `mouseover` event handlers
- Apply selected-item border styling to transitions, as well as clips

(I hate when it has a point.)

ngClass supports an object as argument, each key for which the value
evaluates to true will be used as a class name.

…bengine-box-model

- New 32x32 cursors (which fit new Chrome/Firefox restrictions) will
  show the dashed line only when hovering over clips/transitions, just
  the "knife" part otherwise
- New reveal logic relies on setting a class on the body element, seems
  to style things appropriately. Some UI elements (resize handles, the
  playhead) will show other cursors, if still active in razor mode.
- The (re-laid-out) debug panel now includes a razor mode toggle.