Implement Trash directory

Intended behavior:

• The Trash directory should show all files with trashed = true on Drive.
• Removing a file (unlink) from any directory mark it as trashed.
• Moving a file (rename) from any directory to Trash should mark it as trashed (f273d25).
• Removing a file (unlink) from Trash should delete it permanently (bd528c31d8253d9c28d24bf3817f76f864790e23, 11ebeb65443c1516a0e1f31275906cd47e83d130)
• Moving a file (rename) from Trash to anywhere else should mark the file as not trashed and possibly update its parent.
• Recursively removing a directory (rm -r) should preserve the hierarchy of its content even when moved to Trash