Continuous recipe learning

This PR changes the behavior of learning recipes from books that no longer grant skills.

This allows reading continuously, until all recipes available for current skill levels are learned.
Similarly to how normal book reading currently works, answering 'n' to "do you want to learn from book?" reads the book once, maybe teaching a single recipe.
Copypaste from skillbook reading allows rooters to root while reading recipes.

Normal skillbook and funbook reading is unaffected by the changes, they'll only be visible when reading books that no longer grant skills.

I also nailed a tiny bug that no one would ever notice - reading a useless (possibly fun) skillbook would ask for confirmation twice.