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)

plume-common/src/activity_pub/inbox.rs

@@ -0,0 +1,41 @@
+use activitypub::{Object, activity::Create};
+
+use activity_pub::Id;
+
+#[derive(Fail, Debug)]
+pub enum InboxError {
+    #[fail(display = "The `type` property is required, but was not present")]
+    NoType,
+    #[fail(display = "Invalid activity type")]
+    InvalidType,
+    #[fail(display = "Couldn't undo activity")]
+    CantUndo
+}
+
+pub trait FromActivity<T: Object, C>: Sized {
+    fn from_activity(conn: &C, obj: T, actor: Id) -> Self;
+
+    fn try_from_activity(conn: &C, act: Create) -> bool {
+        if let Ok(obj) = act.create_props.object_object() {
+            Self::from_activity(conn, obj, act.create_props.actor_link::<Id>().unwrap());
+            true
+        } else {
+            false
+        }
+    }
+}
+
+pub trait Notify<C> {
+    fn notify(&self, conn: &C);
+}
+
+pub trait Deletable<C> {
+    /// true if success
+    fn delete_activity(conn: &C, id: Id) -> bool;
+}
+
+pub trait WithInbox {
+    fn get_inbox_url(&self) -> String;
+
+    fn get_shared_inbox_url(&self) -> Option<String>;
+}