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/setup.rs

@@ -7,12 +7,12 @@ use std::path::Path;
 use std::process::{exit, Command};
 use rpassword;
 
-use DB_URL;
-use db_conn::DbConn;
-use models::instance::*;
-use models::users::*;
-
-pub type PgPool = Pool<ConnectionManager<PgConnection>>;
+use plume_models::{
+    DB_URL,
+    db_conn::{DbConn, PgPool},
+    instance::*,
+    users::*
+};
 
 /// Initializes a database pool.
 fn init_pool() -> Option<PgPool> {