feat(web): eliminate the "wait box"

**Is your feature request related to a problem? Please describe.**
When a keyboard is slow to load or has a problem loading, KeymanWeb displays its own UI box which is kinda (okay really, really) ugly and has a poor UX to boot. Dealing with performance and errors should be the domain of site owner and not KeymanWeb.

**Describe the solution you'd like**
Propose eliminating the wait box entirely (perhaps reimplement on keymanweb.com for purposes of example) and adding an event that the implementer can listen to if they want to provide feedback to the user.

**Additional context**
See also https://community.software.sil.org/t/why-does-kmw-wait-box-window-pop-up/2012/4