Adjust implicit permlink generation

The following discussion from !111 (merged) should be addressed:

• @bwrona started a discussion:

  Implicit permlink generation should be moved to:

  • ArticleBuilder constructor (if we want to support it there) and should be based on author and Date i.e.: article-${Date.now()}, otherwise let's add throw if a trimmed permlink is empty
  • ReplyBuilder constructor where is is based on parentAuthor and re- pattern as currently proposed.