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

this was btn-cancel (rather than the text-content, "Cancel") because there are potentially two "Cancel" buttons, one for cancelling the Edit URL, and one for cancelling the Restart Hangout.  I wanted to avoid problems from this ambiguity by using the button's ID.