New User experience

# Changes 

## .png's
* added placeholder screenshots for new user welcome

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## *.js
* changed the initialize from `$('.app-container').append(this.el)` to `$('.app-container').html(this.el)` in <strong>all</strong> views to blow up any left behind content

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## index.html
* added templates for the new user view
* added template for visiting a group before the data has populated

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## app-router.js
* added new route for user experience

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## group-view.js
* added function to render placeholder copy if user attempts to view group before cloud code has updated it
* added function to render warning/direction if you visit a group link that doesn't exist

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## new-user-welcome-view.js
* created new view to walk users through what they can do with the app. appears after sign up is successful, however can be visited at any time.

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## sign-in-view.js
* removed enableEnter function as it was causing the parse "sign in" event to be sent as many times as the keyboard was pressed while in the view
* added a reroute to the dashboard if the user is already signed in

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## sign-up-view.js 
* removed enableEnter function as it was better as stand alone keypress event within the initialize

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## main.scss
* added welcome view styling to import list