Add class to extended pages section

[medienbaecker]

Right now I use the field name as the css selector because I want to keep the pages section as close to the core as possible.

It would be better to add a k-modules-section class somehow.

[medienbaecker]

@mullema on Slack: "You could go down the hacky way and add the class dynamically"

mounted() {
  this.$nextTick(() => {
    this.$el.classList.add('k-modules-section');
  })
}

👌