Buffer: Fix concat()
Buffer: Fix flatMapCh()
Channel: Make partialBiMap() more general
Widget: Add a custom default element in select boxes
Widget: Restore selection after a row gets reinserted
Add implicits to render widget buffers
Widget: Display hidden widgets on the same line
Buffer: Instantiate MapFunctions with references
Widget: Implement widgets that can be inlined

In some situations a designated <span> may have undesired effects.
This will prevent some design glitches and improve the performance
by creating fewer nodes in the DOM.
HTML: Add widget for file uploads