Move main.rs to bin/ and stub some message stuff.

server/src/nm.rs

@@ -0,0 +1,13 @@
+use shared::Message;
+
+use crate::error;
+
+// TODO(wathiede): decide good error type
+pub fn threadset_to_messages(
+    thread_set: notmuch::ThreadSet,
+) -> Result<Vec<Message>, error::ServerError> {
+    for t in thread_set.0 {
+        for tn in t.0 {}
+    }
+    Ok(Vec::new())
+}