tgui: MIT License (#50969)

* MIT license headers

* various tweaks

- Tweak jsdoc headers a bit
- Use an old-school format with SPDX-License-Identifier for SCSS
- Add headers to tgui dmcode

* Simplify the license section

* Rebuild tgui, small tweaks

Co-authored-by: ZeWaka <zewakagamer@gmail.com>

About The Pull Request

All relevant source code now contains copyright headers, that explicitly assert copyright and license for every file.

This has been done to prepare TGUI for wider adoption. Goon station devs are interested in using TGUI, and hopefully this will result in a nice collaboration and improvements to both codebases.

The following files were relicensed under MIT:

    code/controllers/subsystem/tgui.dm
    code/modules/tgui/*.dm
    tgui/**/*.js
    tgui/**/*.scss

The following files were kept untouched:

    tgui/packages/tgui/interfaces/**/*.js
    tgui/packages/tgui/styles/interfaces/**/*.scss

Project is still basically AGPL-3.0 under /tg/station's parent license (with added MIT texts), but allows importing MIT code into MIT-compatible codebases.

tgui/packages/tgui-dev-server/webpack.js

@@ -1,3 +1,9 @@
+/**
+ * @file
+ * @copyright 2020 Aleksej Komarov
+ * @license MIT
+ */
+
 import { createLogger } from 'common/logging.js';
 import fs from 'fs';
 import { createRequire } from 'module';