Added webpack bundling

[SaFrMo]

I was working on learning more about WebDB and wanted a self-contained bundle of this library, so I added a simple npm run bundle command that exports the whole thing into a var called WebDB under dist/bundle.js. Just wanted to submit the PR in case this was useful at all - no problem if not!

[pfrazee]

Nice! I'll try this out and if it looks good, I'll probably merge it with the goal of putting the bundle in the git repo (but NOT in npm) so that folks can get an easy-to-use build from the repo