Avoid panics (#392)

- Use `Result` as much as possible
- Display errors instead of panicking

TODO (maybe in another PR? this one is already quite big):
- Find a way to merge Ructe/ErrorPage types, so that we can have routes returning `Result<X, ErrorPage>` instead of panicking when we have an `Error`
- Display more details about the error, to make it easier to debug

(sorry, this isn't going to be fun to review, the diff is huge, but it is always the same changes)

plume-models/src/comment_seers.rs

@@ -3,7 +3,7 @@ use diesel::{self, ExpressionMethods, QueryDsl, RunQueryDsl};
 use comments::Comment;
 use schema::comment_seers;
 use users::User;
-use Connection;
+use {Connection, Error, Result};
 
 #[derive(Queryable, Serialize, Clone)]
 pub struct CommentSeers {
@@ -22,11 +22,11 @@ pub struct NewCommentSeers {
 impl CommentSeers {
     insert!(comment_seers, NewCommentSeers);
 
-    pub fn can_see(conn: &Connection, c: &Comment, u: &User) -> bool {
-        !comment_seers::table.filter(comment_seers::comment_id.eq(c.id))
+    pub fn can_see(conn: &Connection, c: &Comment, u: &User) -> Result<bool> {
+        comment_seers::table.filter(comment_seers::comment_id.eq(c.id))
             .filter(comment_seers::user_id.eq(u.id))
             .load::<CommentSeers>(conn)
-            .expect("Comment::get_responses: loading error")
-            .is_empty()
+            .map_err(Error::from)
+            .map(|r| !r.is_empty())
     }
 }