Added minimal sdk, simplified test using the sdk's client

ubisync-sdk/src/error.rs

@@ -0,0 +1,20 @@
+use std::fmt::Display;
+
+
+
+#[derive(Debug)]
+pub enum UbisyncError {
+    InvalidNodeReply(String),
+    AppRegistrationFailed,
+}
+
+impl Display for UbisyncError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::InvalidNodeReply(msg) => write!(f, "Invalid reply from ubisync node: {}", msg),
+            Self::AppRegistrationFailed => write!(f, "Registrating this app at the ubisync node failed."),
+        }
+    }
+}
+
+impl std::error::Error for UbisyncError {}