Upgrade handlebars and allow for proper imports of .hbs files

[mgramigna]

Templates are just .ts files right now. We also are using @types/handlebars, but new versions of handlebars export their own types.

Could even consider alternatives to handlebars like ejs if it ends up being a better solution

[mgramigna]

Note that handlebars also causes this warning in webpack-based frontend apps: