Encrypt content sent to the server

This implements client-side encryption, so that users' task information
is not availble to the server (or to anyone who does not have the
`encryption_secret`).

taskchampion/src/server/mod.rs

@@ -16,8 +16,10 @@ pub use types::*;
 pub fn from_config(config: ServerConfig) -> Fallible<Box<dyn Server>> {
     Ok(match config {
         ServerConfig::Local { server_dir } => Box::new(LocalServer::new(server_dir)?),
-        ServerConfig::Remote { origin, client_id } => {
-            Box::new(RemoteServer::new(origin, client_id))
-        }
+        ServerConfig::Remote {
+            origin,
+            client_id,
+            encryption_secret,
+        } => Box::new(RemoteServer::new(origin, client_id, encryption_secret)),
     })
 }