Complete carousel refactor.

Reduces one layer of DOM nesting for simplication, uses the latest Embla
version, unittests for everything.

src/scss/viewer-carousel.scss

@@ -1,6 +1,8 @@
 :host {
   // Center unseekable icon.
   position: relative;
+
+  --video-max-height: none;
 }
 
 // If the carousel has an unselected attribute set on it, do not let the
@@ -8,17 +10,16 @@
 // when the carousel is part of a media-grid. Without this next/prev controls
 // will enlarge on hover, and the wheel-gestures plugin may block scrolling.
 // See matching in live-carousel.scss .
-:host([unselected]) frigate-card-media-carousel,
-:host([unselected]) .seek-warning
-{
+:host([unselected]) frigate-card-carousel,
+:host([unselected]) .seek-warning {
   pointer-events: none;
 }
 
-:host([unseekable]) frigate-card-media-carousel {
+:host([unseekable]) frigate-card-carousel {
   filter: brightness(50%);
 }
 :host([unseekable]) .seek-warning {
-  display: block
+  display: block;
 }
 
 .seek-warning {