feat(web): support for .kmp packages

**Is your feature request related to a problem? Please describe.**
At present, we have to support extra infrastructure to serve JS files for use with the KeymanWeb engine. What if we could just use .kmp files instead?

This becomes even more worth considering if we start adding features easily facilitated by receiving package files, such as UI for specifying keyboard options. We should probably keep help separate, though - lots of parsing would be required to manage page resources for any webpages based within the compressed file.

**Describe the solution you'd like**
JSZip (https://stuk.github.io/jszip/ ) is dual licensed, with one of those being MIT. It has a browser-oriented distributed form and a pretty handy API. ([Some good overview examples may be seen here.](https://stuk.github.io/jszip/documentation/examples.html)) Said API is `Promise`-based, so user interactivity wouldn't be impeded.