[WIP] introduce /dav/spaces endpoint && CS3 list spaces implementation (ocis driver only)

[butonic]

initial implementation for listing storage spaces

• currently lists
  • user homes as type personal spaces
  • shares as type share spaces
  • if /spaces dir does not exist in the metadata it will iterate over all nodes to create the spaces for migration
• create a share space when creating a share
• create a personal space when creating a home
  • refactor CreateHome
• generic create space
• delete share space on unsharing
• delete personal in deprovisioning a user
  • and all contained shares
• delete share space on deleting a folder for all children
• generic delete space
  • share is special because it should not delete the underlying items. Do we need to differentiate between spaces and sub spaces? eg when a user created a new project space from his personal space? or do we move it out of it and really manage it as a dedicated space? Should we manage share spaces in the same way? at least for ocis we could ... would be too theoretical imo.

[update-docs]

Thanks for opening this pull request! The maintainers of this repository would appreciate it if you would create a changelog item based on your changes.

[butonic]

cc @dragotin

[C0rby]

All method handlers are implemented. I guess the next step is to refactor/deduplicate the code.

[butonic]

superseded by #1776