Filehandling overwrite dialog

See merge request !1

# Conflicts:
#   packages/file-handling/src/dbp-nextcloud-file-picker.js

Merge branch 'filehandling-overwrite-dialog' of gitlab.tugraz.at:dbp/web-components/toolkit into filehandling-overwrite-dialog

it's unused atm

Instead of hardcoding the paths of the node_modules directory we use the node-resolve
plugin of rollup to find the root of the corresponding JS package and calcucate a path from
there.

Resolving a package requires calling an async function, so we have to use await in the rollup config.
Luckily rollup supports configs wrapped in a promise, so we just have to wrap it in a function which returns
a promise.