Allow subscription to be created and deleted without refreshing page

https://trello.com/c/l2vLI2yj/353-address-repos-with-subscriptions-that-weren-t-enabled
Allow non-paying users to unsubscribe

https://trello.com/c/SrdebCDE/345-ensure-that-only-repo-payer-can-disable-it
Add JavaScript support

https://trello.com/c/LQsUqhYU/179-support-javascript

* Use JSHint to review JavaScript code
* Allow users to configure JavaScript style guide
* Use jshintrb gem to easily use JSHint in Ruby
Fix style guides link
Specify indentation preference for JavaScript
Merge pull request #405 from soulcutter/patch-1

Update style guide path.
Fix client/server-side analytics race condition

We are seeing bad analytics data in Mixpanel because
we are not aliasing guests into users.

https://mixpanel.com/docs/integration-libraries/using-mixpanel-alias

Segment.io strongly recommends doing this client-side:

https://segment.io/docs/integrations/mixpanel/#alias

Restrict user-facing flash messages to a known whitelist
so we don't accidentally send `flash[:signed_up]` to the view.

https://trello.com/c/ZzJdRvJu
Update tagline to include JavaScript, CoffeeScript
Merge remote-tracking branch 'upstream/master'

Conflicts:
	README.md
	app/assets/javascripts/directives/repo.js.coffee.erb
	app/controllers/subscriptions_controller.rb
	app/models/repo_config.rb
	app/views/application/_segment_io.html.erb
	app/views/application/configuration.haml
	app/views/layouts/application.haml
	app/views/sessions/new.haml
	app/views/shared/_intercom_settings.haml
	spec/controllers/deactivations_controller_spec.rb
	spec/controllers/subscriptions_controller_spec.rb
	spec/models/style_checker_spec.rb