Use ES Class Fields & Static Properties (currently stage 2) for improve class outlook.

Added babel-plugin-transform-class-properties as a Babel plugin.

* ui: check spoiler_text against regex filter (#1635)

When filtering by regex, also check the spoiler_text if
present.

* ui: concatenate spoiler and content in reducer

Simplifies aa5b03c, clarifies intent of the field

* Replace browserify with webpack

* Add react-intl-translations-manager

* Do not minify in development, add offline-plugin for ServiceWorker background cache updates

* Adjust tests and dependencies

* Fix production deployments

* Fix tests

* More optimizations

* Improve travis cache for npm stuff

* Re-run travis

* Add back support for custom.scss as before

* Remove offline-plugin and babili

* Fix issue with Immutable.List().unshift(...values) not working as expected

* Make travis load schema instead of running all migrations in sequence

* Fix missing React import in WarningContainer. Optimize rendering performance by using ImmutablePureComponent instead of
React.PureComponent. ImmutablePureComponent uses Immutable.is() to compare props. Replace dynamic callback bindings in
<UI />

* Add react definitions to places that use JSX

* Add Procfile.dev for running rails, webpack and streaming API at the same time