Return correct Errors and replace panic, fix misc review issues

Remove EventJson todo comments, clean up Cargo.toml commented ruma deps.

src/database/globals.rs

@@ -32,7 +32,7 @@ impl Globals {
                     .unwrap_or("localhost")
                     .to_owned(),
             )
-            .map_err(|_| Error::bad_database("Invalid server name"))?,
+            .map_err(|_| Error::BadConfig("Invalid server name"))?,
             registration_disabled: config.get_bool("registration_disabled").unwrap_or(false),
         })
     }

src/database/rooms/edus.rs

@@ -62,8 +62,6 @@ impl RoomEdus {
         room_id: &RoomId,
         since: u64,
     ) -> Result<impl Iterator<Item = Result<EventJson<EduEvent>>>> {
-        // TODO is this                                ^^^^^^^
-        // only ever a read receipt could we just return EphemeralRoomEvent here?
         let mut prefix = room_id.to_string().as_bytes().to_vec();
         prefix.push(0xff);