Rewrite article publication with the REST API

- Add a default App and ApiToken for each user, that is used by the front-end
- Add an API route to update an article (CSRF had to be disabled because of a bug in rocket_csrf)
- Use AJAX to publish and edit articles in the new editor, instead of weird hacks with HTML forms

plume-api/src/posts.rs

@@ -28,4 +28,5 @@ pub struct PostData {
     pub license: String,
     pub tags: Vec<String>,
     pub cover_id: Option<i32>,
+    pub url: String,
 }