WebDAV: remove notifications, timeout logic (#1630)

* Refactor openDocument operation to use OsConstants for mode parsing

* RandomAccessCallbackWrapper: refactor so that it's only purpose is to avoid the memory leak

* Use main looper instead of a new thread per RandomAccessCallback

* Remove WebDAV access notification

* Remove nsk90-kstatemachine dependency

* Simplify fileDescriptor() method

* Use dedicated I/O thread again; use Kotlin `copyTo` for copying