Hangouts feature - hangout setup flow cleanup

`events show view`: added buttons for restarting the hangout and editing the link manually
`hangouts controller`: updated to allow local requests to update hangouts url
`hangouts.js`: 
- move all the hangouts logic into one .js file.  
- removed events.js and removed hangouts code from projects.js.  No precompilation of those files is needed anymore.
- changed the initializer of hangout load the HangoutConnection app only for the user that started the ho.

some refactoring of html and css is needed.

demo at: yaro.herokuapp.com

`return unless Features.enabled?(:slack_notifications)`