Big repository reorganization

The code is divided in three crates:
- plume-common, for the ActivityPub module, and some common utils
- plume-models, for the models and database-related code
- plume, the app itself

This new organization will allow to test it more easily, but also to create other tools that only reuse a little part of
the code (for instance a Wordpress import tool, that would just use the plume-models crate)

src/routes/comments.rs

@@ -4,15 +4,16 @@ use rocket::{
 };
 use serde_json;
 
-use activity_pub::{broadcast, inbox::Inbox};
-use db_conn::DbConn;
-use models::{
+use plume_common::activity_pub::broadcast;
+use plume_models::{
     blogs::Blog,
     comments::*,
+    db_conn::DbConn,
     instance::Instance,
     posts::Post,
     users::User
 };
+use inbox::Inbox;
 
 #[derive(FromForm)]
 pub struct CommentQuery {