Cleanup ReadableLogChannel and LogVersionedStoreChannel interfaces

- Rationale:
  there is obviously some conflation between ReadableLogChannel and LogVersionedStoreChannel interfaces -
  neither purpose is clear and while the functionality they provide is necessary, it is not abstracted correctly.

- Details:
  This PR tries to cleanup those interfaces by extracting and isolating the different abstractions in them, e.g.,
  decoupling the getCurrentPosition and getVersion/getFormatVersion from the read API in ReadableLogChannel.

  It also introduces more specialised interfaces like ReadableVersionableLogChannel which exposes log version
  information when necessary, i.e., when the channel is backed by a log file on disk. In this way we can clean
  up other implementations, like NetworkReadableLogChannel which does not contain log version info.

  Finally, a factory has been introduce to simplify the creation of LogEntryReaders according to the use case.