Use Twig

[samdark]

We should try to implement Twig templates in the app.

Main benefit is that it provides output escaping out of the box so there will be way less Yii 3 apps with XSS. Another thing is that it's a good idea to try using Twig with widgets and classes we have.

[kaznovac]

consider plates instead of twig (performance seems considerably better than twig's according to this test http://www.phpbenchmarks.com/en/comparator/templating)

[samdark]

@kaznovac we have our own support for PHP templates so using plates with Yii3 doesn't make sense.