MYLOC-86 - Displaying a cold start message

Involves:
- refactoring the dialog out into a new component
- updating user_locations to use the component
- updating the primary controller to display a dialog when required
- setting a cookie to remember when users have said 'no'

The conditions under which the message are displayed are tested in shouldColdStartDialogBeDisplayed(). 
I created a core js cookie module to support this. We should probably use the cookies.isSupported method in order to decide if the prefer 'star' is displayed to people.