Media server support

Still only works for clients and is not federated. Need to figure out
caching when I get to the federated version

src/main.rs

@@ -79,6 +79,17 @@ async fn main() -> ExitCode {
         tracing_subscriber::fmt().with_max_level(level).finish()
     ).expect("Failed to setup logger");
 
+    // Check to make sure media directory exists
+    match std::fs::exists(&config.media_directory) {
+        Ok(true) => {},
+        // NOTE: maybe shouldnt shadow this error
+        _ => {
+            error!("Media directory {} does not exist. Check to make sure it is a directory and is writable.",config.media_directory);
+            return ExitCode::FAILURE;
+        }
+
+    }
+
 
     // Set up database connection
     let db_string = format!("postgres://{}:{}@{}/{}",config.database.user,config.database.password,config.database.url,config.database.db_name);