Update repository URLs to nextgen-networks while preserving deep links

Replaced bare references to the-djmaze/snappymail with nextgen-networks/snappymail/
and updated .git URLs to the new organization.

Per user request:
- README files are excluded.
- URLs with a trailing slash (e.g. issues, pull requests, releases) are
  left pointing to the original repository to preserve historical context.
- Bare web URLs now include the requested trailing slash.
- Existing nextgen-networks bare URLs were updated to include the trailing slash.

Co-authored-by: nextgen-networks <21206978+nextgen-networks@users.noreply.github.com>

dev/Remote/AbstractFetch.js

@@ -47,7 +47,7 @@ fetchJSON = (action, sUrl, params, timeout, jsonCallback) => {
 			params.Action = action;
 		}
 	}
-	// Don't abort, read https://github.com/nextgen-networks/snappymail/issues/487
+	// Don't abort, read https://github.com/the-djmaze/snappymail/issues/487
 //	abort(action, 0, 1);
 	const controller = new AbortController(),
 		signal = controller.signal;