Try to hack collapsing columns, make modal menu scrollable on mobile phones, add remember me button to nextcloud

Upload was broken without any error with webdav-client 4.x. This was
hiding the error.

This option doesn't exist in webdav.client 3.x but is required in 4.x
due to https://github.com/perry-mitchell/webdav-client/issues/266

This will switching between versions easier.

Allow globally overriding slots in the light dom of components and use it to override the auth-info slot in the Nextcloud file picker