Increase copy limit

[spaenleh]

We have had reports of users unable to copy their content because they have more than the current 130 descendants in thier lesson.

A reasonable course can have around 300 items, and dependeing on how much content is alternating between text and images, videos, links for example, it can grow to more than 500.

Increasing the limit to 400 would be a good first step to allow users to copy their courses where they need.