This allows using rspec with `--only-failures`

Adopted from GitLab CE. Generate new migration with:

    rails g post_deployment_migration name_of_migration_here

By default they are run together with db:migrate. To not run them,
the env variable SKIP_POST_DEPLOYMENT_MIGRATIONS must be set

Code by Yorick Peterse <yorickpeterse@gmail.com>, see also:

83c8241160

* 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