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

plume-models/src/lib.rs

@@ -235,9 +235,9 @@ macro_rules! get {
 /// ```
 macro_rules! insert {
     ($table:ident, $from:ident) => {
-        insert!($table, $from, |x, _conn| { Ok(x) });
+        insert!($table, $from, |x, _conn| Ok(x));
     };
-    ($table:ident, $from:ident, |$val:ident, $conn:ident | $after:block) => {
+    ($table:ident, $from:ident, |$val:ident, $conn:ident | $( $after:tt )+) => {
         last!($table);
 
         pub fn insert(conn: &crate::Connection, new: $from) -> Result<Self> {
@@ -247,7 +247,7 @@ macro_rules! insert {
             #[allow(unused_mut)]
             let mut $val = Self::last(conn)?;
             let $conn = conn;
-            $after
+            $( $after )+
         }
     };
 }
@@ -310,8 +310,8 @@ mod tests {
     }
 
     pub fn db() -> Conn {
-        let conn =
-            Conn::establish(CONFIG.database_url.as_str()).expect("Couldn't connect to the database");
+        let conn = Conn::establish(CONFIG.database_url.as_str())
+            .expect("Couldn't connect to the database");
         embedded_migrations::run(&conn).expect("Couldn't run migrations");
         #[cfg(feature = "sqlite")]
         sql_query("PRAGMA foreign_keys = on;")