Write `get-file` and commands to get the list of blocks from another node

Description

This closes #1 (closed) by providing an API that allows to get a file with just its hash

Detailed list of changes

• add get_file, get_blocks_info_from and other things related to managing the filesystem
• add new commands to nu API
• remove DragoonBehaviour as it was not useful
• add two new tests for get_file and change the already existing test to use the new API

Note

The get_file is still very rough, the error management needs to be handled better to take into a lot more cases of failure

src/dragoon_network.rs

-use anyhow::{self, Result};
 use anyhow::{self, format_err, Result};
 use futures::prelude::*;
 use futures::stream::BoxStream;
@@ -126,6 +125,7 @@ pub(crate) struct DragoonBehaviour {
 pub(crate) struct DragoonNetwork {
     swarm: Swarm<DragoonBehaviour>,
     command_receiver: mpsc::UnboundedReceiver<DragoonCommand>,
+    command_sender: mpsc::UnboundedSender<DragoonCommand>,
     listeners: HashMap<u64, ListenerId>,
     file_dir: PathBuf,
     pending_start_providing: HashMap<kad::QueryId, Sender<()>>,
@@ -138,12 +138,14 @@ impl DragoonNetwork {
     pub fn new(
         swarm: Swarm<DragoonBehaviour>,
         command_receiver: mpsc::UnboundedReceiver<DragoonCommand>,
+        command_sender: mpsc::UnboundedSender<DragoonCommand>,
         peer_id: PeerId,
         replace: bool,
     ) -> Self {
         Self {
             swarm,
             command_receiver,
+            command_sender,
             listeners: HashMap::new(),
             file_dir: Self::create_block_dir(peer_id, replace).unwrap(),
             pending_start_providing: Default::default(),