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/Settings/User/Security.js

@@ -77,7 +77,7 @@ export class UserSettingsSecurity extends AbstractViewSettings {
 		 */
 		window.mailvelope && mailvelope.createSettingsContainer('#mailvelope-settings'/*[, keyring], options*/);
 		/**
-		 * https://github.com/nextgen-networks/snappymail/issues/973
+		 * https://github.com/the-djmaze/snappymail/issues/973
 		Remote.request('GetStoredPGPKeys', (iError, data) => {
 			console.dir([iError, data]);
 		});