Restore Trash Integration

[i2h3]

The trash feature is removed temporarily due to its implementation. We have reviewed the current implementation and heard the feedback about it and decided to reimplement it with a consistent behavior. We intend to ship that with the next bigger release.

• Trash integration is always and permanently enabled. There is no user choice anymore. Not just for simplicity but also to not mess up local and remote file system state due to the possible change. The only exception to this: the server does not support item trashing.
• Only items moved to the trash on the same device are listed in the local trash. Items which already were in the remote trash before are explicitly excluded. Also, any items from group folders or owned by others are also excluded. They show up in the Nextcloud web user interface but they have no relation to the local trash of the user's device. And it is a known and undesired behavior that a local trash purge also permanently removes remote items deleted by others in shared folders. This is not something user's have in mind and expect when emptying their local device trash.
• This requires changes to the data scheme to track which item was deleted by the local user on the local device. This also is one of the reasons for the intermediate feature removal instead of a fix because the underlying data management is supposed to change drastically (Replace Realm with CoreData #9046).