.editorconfig: Makefile uses tabs
Add uglify to development dependencies
Add dist task to generate production assets

 * ignore `dist/`
 * copy `i18n.js` and `i18n-plurals.js` to `dist/`
 * use `uglify` to generate `.min.js` versions
Use Ember.Handlebars, not window.Handlebars

Ember no longer requires a runtime version of Handlebars. The only
place we were using `window.Handlebars` was for `Handlebars.SafeString`,
which we were using only *inconsistently*. Instead, use
`Ember.Handlebars.SafeString` and get rid of `PlainHandlebars`, our
alias for `window.Handlebars`.

Resolves #181