Tag selector performance overhaul

- Use react-virtualized to render tags on demand, reducing the number
  of DOM elements from potentially tens of thousands to <100. This
  requires tags to be absolutely positioned, so sizing and
  positioning need to be precomputed rather than relying on CSS.
- Avoid unnecessary refreshes, speed up tag retrieval, and optimize
  sorting
- Debounce reflowing when resizing tag selector

Also:

- Scroll to top when changing collections
- Allow tags to take up full width of tag selector without truncation

Closes #1649
Closes #281

scripts/config.js

@@ -31,6 +31,7 @@ const symlinkFiles = [
 	'resource/**/*',
 	'!resource/react.js',
 	'!resource/react-dom.js',
+	'!resource/react-virtualized.js',
 	'update.rdf'
 ];
 
@@ -64,6 +65,7 @@ const jsFiles = [
 	// Special handling for React -- see note above
 	'resource/react.js',
 	'resource/react-dom.js',
+	'resource/react-virtualized.js',
 ];
 
 const scssFiles = [