Feature/vue3 upgrade

[marcelTUB]

Preparations for upgrading vue2 to vue3

• upgrade vue, vue-cli-service and vue/cli-service plugins

• use migration build

• fix compiler warnings (filters, v-bind, key on template tag, template without directives)

• fix some errors by commenting problematic lines

[schlagtim]

Thanks for your contribution!
It seems like the DCO checks are failing because your commits are not signed off - these commits cannot be merged.
Please read the Contributing document in the root directory, particularly the chapter Sign your work.

Your previous commits (apart from the most recent one) cannot be signed-off anymore. The DCO check will always fail if there is at least one unsigned commit. Possible solutions in this situation are:

• Rewrite your commits git history with git filter-branch and git interpret-trailers: https://stackoverflow.com/a/15667644
• Or squash all commits into one commit and sign-off this commit (e.g. with git --amend). Your history (individual commits) will be lost

Whatever solutions you choose, you will probably have to do a force push to overwrite the history here.

To prevent this in the future you usually can activate a "always sign-off commits" option in your IDE (most of them support it) or git tool which I highly recommend.

[etschelp]

We just found out that the support for data tables will be available with vuetify 3.1 see vuetifyjs/vuetify#13479 (comment)

It will probably be a while until this happens, as we rely heavily on data tables, it probably makes sense to do the following:

• upgrade all plugins
• do the vue3 upgrade
• keep the migration build
• check if the UI keeps running
• merge