Update to vue 2.7.8

[Isokaeder]

Vue "Naruto" is released, making composition api for the greatest part available inside Vue 2.7

This is a naive update to Vue 2.7 and removal of @vue/composition-api, without incremental progression to catch all breaking changes. This is meant as a research and experimentation branch, to answer questions about the best approach to update to vue-v3, and whether we should go there directly or whether vue 2.7 should be an intermediary step.

[render[bot]]

Your Render PR Server URL is https://kotti-pr-652.onrender.com.

Follow its progress at https://dashboard.render.com/static/srv-cbfm5vc6fj35hjsgbfkg.

[FlorianWendelborn]

Wow that’s some great news