restore composer.json, add mysqli extension

public/vendor/editor/.github/CONTRIBUTING.md

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+## Contributing
+* Pull requests are welcome
+* Please `don't include dist/* files` on your commits.
+
+## Coding convention
+* eslint: https://eslint.org
+* eslint rule: https://github.com/summernote/summernote/blob/master/.eslintrc
+
+## Build summernote
+```bash
+npm install
+
+# build full version of summernote: dist/summernote.js
+npm run build
+
+```
+At this point, you should now have a `dist/` directory populated with everything you need to use summernote.
+
+## Start local server for developing summernote.
+run local server with webpack-dev-server and watch.
+```bash
+npm run dev
+# Open a browser on http://localhost:3000.
+# If you change source code, automatically reload your page.
+```
+
+## Test summernote
+run tests with Karma and PhantomJS
+```bash
+npm run test
+```
+If you want run tests on other browser,
+change the values for `browsers` properties in `karma.conf.js`.
+
+```
+karma: {
+  all: {
+    browsers: ['PhantomJS'],
+    reporters: ['progress']
+  }
+}
+
+```
+
+Or, pass `--browsers` argument via `npm run test` command.
+```
+$ npm run test -- --browsers Safari,Firefox
+```
+
+You can use `Chrome`, `ChromeCanary`, `Firefox`, `Opera`, `Safari`, `PhantomJS` and `IE` beside `PhantomJS`.
+Once you run `npm test`, it will watch all javascript file. Therefore karma run tests every time you change code.
+
+## Test a part of test
+
+If you would like to run some part of your test codes, use the watch mode.
+
+```bash
+$ npm run test:watch
+```
+
+`karma` will run test and keep waiting other test requests. And then, run `test:grep` in another terminal. Below shows how to run `LinkDialog` related tests only.
+
+```bash
+$ npm run test:grep LinkDialog
+```
+
+## Prepush Hooks
+As part of this repo, we use the NPM package husky to implement git hooks. We leverage the prepush hook to prevent bad commits.
+
+## Document structure
+
+```
+ - body container: <div class="note-editable">, <td>, <blockquote>, <ul>
+ - block node: <div>, <p>, <li>, <h1>, <table>
+ - void block node: <hr>
+ - inline node: <span>, <b>, <font>, <a>, ...
+ - void inline node: <img>
+ - text node: #text
+```
+
+1. A body container has block node, but `<ul>` has only `<li>` nodes.
+1. A body container also has inline nodes sometimes. This inline nodes will be wrapped with `<p>` when enter key pressed.
+1. A block node only has inline nodes.
+1. A inline nodes has another inline nodes
+1. `#text` and void inline node doesn't have children.