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/sign.rs

@@ -0,0 +1,56 @@
+use base64;
+use chrono::Utc;
+use hex;
+use openssl::{
+    pkey::PKey,
+    rsa::Rsa,
+    sha::sha256
+};
+use serde_json;
+
+/// Returns (public key, private key)
+pub fn gen_keypair() -> (Vec<u8>, Vec<u8>) {
+    let keypair = Rsa::generate(2048).unwrap();
+    let keypair = PKey::from_rsa(keypair).unwrap();
+    (keypair.public_key_to_pem().unwrap(), keypair.private_key_to_pem_pkcs8().unwrap())
+}
+
+pub trait Signer {
+    fn get_key_id(&self) -> String;
+    
+    /// Sign some data with the signer keypair
+    fn sign(&self, to_sign: String) -> Vec<u8>;
+}
+
+pub trait Signable {
+    fn sign<T>(&mut self, creator: &T) -> &mut Self where T: Signer;
+
+    fn hash(data: String) -> String {
+        let bytes = data.into_bytes();
+        hex::encode(sha256(&bytes[..]))
+    }
+}
+
+impl Signable for serde_json::Value {
+    fn sign<T: Signer>(&mut self, creator: &T) -> &mut serde_json::Value {
+        let creation_date = Utc::now().to_rfc3339();
+        let mut options = json!({
+            "type": "RsaSignature2017",
+            "creator": creator.get_key_id(),
+            "created": creation_date
+        });
+
+        let options_hash  = Self::hash(json!({
+            "@context": "https://w3id.org/identity/v1",
+            "created": creation_date
+        }).to_string());
+        let document_hash = Self::hash(self.to_string());
+        let to_be_signed = options_hash + &document_hash;
+
+        let signature = base64::encode(&creator.sign(to_be_signed));
+
+        options["signaureValue"] = serde_json::Value::String(signature);
+        self["signature"] = options;
+        self
+    }
+}