refactor: standardise error messages

src/error.rs

@@ -0,0 +1,13 @@
+#[repr(i32)]
+pub enum ExitCode {
+    GtkDisplay = 1,
+    CreateBars = 2,
+    Config = 3,
+}
+
+pub const ERR_OUTPUTS: &str = "GTK and Sway are reporting a different set of outputs - this is a severe bug and should never happen";
+pub const ERR_MUTEX_LOCK: &str = "Failed to get lock on Mutex";
+pub const ERR_READ_LOCK: &str = "Failed to get read lock";
+pub const ERR_WRITE_LOCK: &str = "Failed to get write lock";
+pub const ERR_CHANNEL_SEND: &str = "Failed to send message to channel";
+pub const ERR_CHANNEL_RECV: &str = "Failed to receive message from channel";