Unicode Emoji Toolbox Plugin

[w8tcha]

This PR is based on

#947

This PR adds optional unicode emoji selector in toolbar as a Plugin. The existing emoticon support may not be fit for all use cases so now the user has option to use unicode emojies or image emoticons.

Use it by adding preferred emojies in SCEditor initialization:

sceditor.create(textarea, {
	format: 'bbcode',
	style: 'https://cdn.jsdelivr.net/npm/sceditor@3/minified/themes/content/default.min.css',
	emojis: ['😊', '❤️', '😄'],
        plugins: 'emojis'
});

If there are no options set it loads the EmojiMart Picker

[samclarke]

Thanks for the PR, looks great! 👍

The style tests were failing so I've added a commit to fix that as it's just changing spaces to tabs and adding a few extra spaces. Also adds a comment to tell ESLint that EmojiMart is a global variable.

Really need to change to using Prettier for the formatting so it can all be automated.

[w8tcha]

Thanks for adding it. I also send a pull request for the website documentation