Universal Links: Handle Editor link

[kwonye]

When the user navigates to the app via a New Post link, we should launch the editor in the app.

https://wordpress.com/post
https://wordpress.com/post/:domain
Considerations:

Is the user logged in?
If the URL contains a reference to a specific site, do we have that site in the app?
Will this link be triggered if the user tries to edit an existing post?
Existing posts link to /post/:domain/:post_id – we should ignore this case for now.