Autocomplete SDK sample

[jacekbogdanski]

We need autocomplete SDK sample. Some requirements:

• single editor, used to insert content from a list of predefined templates
• templates like footer, greetings, common responses
• we could use text without marker, so for instance just typing "wontfix" would bring a "won't fix" template
• dropdown entries should be displayed similarly to GH (https://i.imgur.com/6S8p5K3.png)

See https://github.com/ckeditor/ckeditor-dev/issues/1751