Attach shared and local DBs to temporary main DB

We now have one connection to the temporary main DB instead of one for
each. The two actual databases are attached to it during initialization.

src/persist/data_manager.rs

@@ -74,9 +74,7 @@ impl DataManager {
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub enum DataManagerError {
   NoHomeDir,
-  CannotOpenSharedDB,
-  UnknownSharedDBError,
-  CannotOpenLocalDB,
-  UnknownLocalDBError,
+  CannotOpenDB,
+  UnknownDBError,
   UnknownTextureError,
 }