Edit blogs, and add blog icons and banners (#460)

Also adds a parameter to `md_to_html` to only render inline elements (so that we don't have titles or images in blog descriptions). And moves the delete button for the blog on the edition page.

I still have to update the SQLite migration once others PRs with migrations will be merged.

Also, there will be a problem when you edit a blog while not owning its banner or icon: when validating they will be reset to their default values… I don't see a good solution to this until we have a better way to handle uploads with Rocket (the same is probably happening for articles btw).

And the icon/banner are not federated yet, I don't know if I should add it to this PR or if it can come after?

![image](https://user-images.githubusercontent.com/16254623/53894510-7d853300-4030-11e9-8a2c-f5c0b0c7f512.png)
![image](https://user-images.githubusercontent.com/16254623/53894539-8b3ab880-4030-11e9-8113-685a27be8d7c.png)

Fixes #453
Fixes #454

src/main.rs

@@ -127,7 +127,6 @@ Then try to restart Plume
     })
     .expect("Error setting Ctrl-c handler");
 
-
     let mail = mail::init();
     if mail.is_none() && CONFIG.rocket.as_ref().unwrap().environment.is_prod() {
         println!("Warning: the email server is not configured (or not completely).");
@@ -145,6 +144,8 @@ Then try to restart Plume
                 routes::blogs::new_auth,
                 routes::blogs::create,
                 routes::blogs::delete,
+                routes::blogs::edit,
+                routes::blogs::update,
                 routes::blogs::atom_feed,
                 routes::comments::create,
                 routes::comments::delete,